diff --git a/crates/rrt-runtime/src/inspect/engine_types.rs b/crates/rrt-runtime/src/inspect/engine_types.rs
index e5fb8f8..1b74a93 100644
--- a/crates/rrt-runtime/src/inspect/engine_types.rs
+++ b/crates/rrt-runtime/src/inspect/engine_types.rs
@@ -146,9 +146,11 @@ pub struct EngineTypesInspectionReport {
     pub unmatched_cct_file_count: usize,
     pub car_side_view_resource_counts: BTreeMap<String, usize>,
     pub car_auxiliary_stem_counts: BTreeMap<String, usize>,
+    pub car_auxiliary_stem_relation_counts: BTreeMap<String, usize>,
     pub lco_companion_stem_counts: BTreeMap<String, usize>,
     pub lco_body_type_label_counts: BTreeMap<String, usize>,
     pub cgo_scalar_value_counts: BTreeMap<String, usize>,
+    pub cgo_scalar_ladder_counts: BTreeMap<String, usize>,
     pub cgo_scalar_values_by_content_stem: BTreeMap<String, Vec<String>>,
     pub cct_identifier_counts: BTreeMap<String, usize>,
     pub cct_value_counts: BTreeMap<String, usize>,
@@ -356,6 +358,11 @@ pub fn inspect_engine_types_dir(
             .iter()
             .filter_map(|family| family.auxiliary_stem.as_deref()),
     );
+    let car_auxiliary_stem_relation_counts = count_owned_values(
+        family_entries
+            .iter()
+            .filter_map(classify_car_auxiliary_stem_relation),
+    );
     let lco_companion_stem_counts = count_named_values(
         family_entries
             .iter()
@@ -373,6 +380,8 @@ pub fn inspect_engine_types_dir(
     );
     let cgo_scalar_values_by_content_stem =
         build_cgo_scalar_values_by_content_stem(cgo_reports.values());
+    let cgo_scalar_ladder_counts =
+        build_cgo_scalar_ladder_counts(cgo_scalar_values_by_content_stem.values());
     let cct_identifier_counts = count_named_values(
         family_entries
             .iter()
@@ -428,9 +437,11 @@ pub fn inspect_engine_types_dir(
             .count(),
         car_side_view_resource_counts,
         car_auxiliary_stem_counts,
+        car_auxiliary_stem_relation_counts,
         lco_companion_stem_counts,
         lco_body_type_label_counts,
         cgo_scalar_value_counts,
+        cgo_scalar_ladder_counts,
         cgo_scalar_values_by_content_stem,
         cct_identifier_counts,
         cct_value_counts,
@@ -674,10 +685,34 @@ fn count_owned_values(values: impl Iterator<Item = String>) -> BTreeMap<String,
     counts
 }
 
+fn classify_car_auxiliary_stem_relation(family: &EngineTypeFamilyEntry) -> Option<String> {
+    let auxiliary_stem = family.auxiliary_stem.as_deref()?;
+    let internal_stem = family.internal_stem.as_deref()?;
+    if auxiliary_stem == internal_stem {
+        return Some("matches_internal_stem".to_string());
+    }
+    let internal_without_role_suffix = strip_terminal_role_letter(internal_stem)?;
+    if auxiliary_stem == internal_without_role_suffix {
+        return Some("matches_internal_without_role_suffix".to_string());
+    }
+    if auxiliary_stem.eq_ignore_ascii_case(internal_without_role_suffix) {
+        return Some("matches_internal_without_role_suffix_casefolded".to_string());
+    }
+    Some("distinct_auxiliary_stem".to_string())
+}
+
+fn strip_terminal_role_letter(value: &str) -> Option<&str> {
+    let last = value.chars().last()?;
+    matches!(last, 'L' | 'T' | 'l' | 't').then(|| {
+        let cutoff = value.len() - last.len_utf8();
+        &value[..cutoff]
+    })
+}
+
 fn build_cgo_scalar_values_by_content_stem<'a>(
     reports: impl Iterator<Item = &'a EngineTypeCgoInspectionReport>,
 ) -> BTreeMap<String, Vec<String>> {
-    let mut grouped = BTreeMap::<String, Vec<String>>::new();
+    let mut grouped = BTreeMap::<String, Vec<f32>>::new();
     for report in reports {
         let Some(content_stem) = report.content_stem.as_ref() else {
             continue;
@@ -688,13 +723,28 @@ fn build_cgo_scalar_values_by_content_stem<'a>(
         grouped
             .entry(content_stem.clone())
             .or_default()
-            .push(format!("{leading_f32:.6}"));
-    }
-    for values in grouped.values_mut() {
-        values.sort();
-        values.dedup();
+            .push(leading_f32);
     }
     grouped
+        .into_iter()
+        .map(|(content_stem, mut values)| {
+            values.sort_by(f32::total_cmp);
+            values.dedup();
+            (
+                content_stem,
+                values
+                    .into_iter()
+                    .map(|value| format!("{value:.6}"))
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .collect()
+}
+
+fn build_cgo_scalar_ladder_counts<'a>(
+    ladders: impl Iterator<Item = &'a Vec<String>>,
+) -> BTreeMap<String, usize> {
+    count_owned_values(ladders.map(|ladder| ladder.join(" -> ")))
 }
 
 #[cfg(test)]
@@ -824,9 +874,8 @@ mod tests {
 
     #[test]
     fn counts_directory_level_slot_values() {
-        let counts = count_named_values(
-            ["CarSideView_1.imb", "CarSideView_1.imb", "VL80T"].into_iter(),
-        );
+        let counts =
+            count_named_values(["CarSideView_1.imb", "CarSideView_1.imb", "VL80T"].into_iter());
         assert_eq!(counts.get("CarSideView_1.imb"), Some(&2));
         assert_eq!(counts.get("VL80T"), Some(&1));
     }
@@ -868,9 +917,73 @@ mod tests {
         );
     }
 
+    #[test]
+    fn classifies_car_auxiliary_stem_relations() {
+        let identical = EngineTypeFamilyEntry {
+            canonical_stem: "gp7".to_string(),
+            car_file: None,
+            lco_file: None,
+            cgo_file: None,
+            cct_file: None,
+            primary_display_name: None,
+            content_name: None,
+            internal_stem: Some("GP7L".to_string()),
+            auxiliary_stem: Some("GP7L".to_string()),
+            side_view_resource: None,
+            companion_stem: None,
+            body_type_label: None,
+            cct_identifier: None,
+            cct_value: None,
+            has_matched_locomotive_pair: false,
+        };
+        let stripped = EngineTypeFamilyEntry {
+            internal_stem: Some("Class01L".to_string()),
+            auxiliary_stem: Some("Class01".to_string()),
+            ..identical.clone()
+        };
+        let stripped_casefolded = EngineTypeFamilyEntry {
+            internal_stem: Some("classqjt".to_string()),
+            auxiliary_stem: Some("qjclasst".to_string()),
+            ..identical.clone()
+        };
+        let distinct = EngineTypeFamilyEntry {
+            internal_stem: Some("ClassA1T".to_string()),
+            auxiliary_stem: Some("ClassA1L".to_string()),
+            ..identical
+        };
+
+        assert_eq!(
+            classify_car_auxiliary_stem_relation(&stripped),
+            Some("matches_internal_without_role_suffix".to_string())
+        );
+        assert_eq!(
+            classify_car_auxiliary_stem_relation(&stripped_casefolded),
+            Some("distinct_auxiliary_stem".to_string())
+        );
+        assert_eq!(
+            classify_car_auxiliary_stem_relation(&distinct),
+            Some("distinct_auxiliary_stem".to_string())
+        );
+    }
+
+    #[test]
+    fn builds_cgo_scalar_ladder_counts() {
+        let ladders = build_cgo_scalar_ladder_counts(
+            [
+                vec!["10.000000".to_string(), "20.000000".to_string()],
+                vec!["10.000000".to_string(), "20.000000".to_string()],
+                vec!["55.000000".to_string(), "85.000000".to_string()],
+            ]
+            .iter(),
+        );
+        assert_eq!(ladders.get("10.000000 -> 20.000000"), Some(&2));
+        assert_eq!(ladders.get("55.000000 -> 85.000000"), Some(&1));
+    }
+
     #[test]
     fn counts_owned_value_strings() {
-        let counts = count_owned_values(["13".to_string(), "13".to_string(), "4".to_string()].into_iter());
+        let counts =
+            count_owned_values(["13".to_string(), "13".to_string(), "4".to_string()].into_iter());
         assert_eq!(counts.get("13"), Some(&2));
         assert_eq!(counts.get("4"), Some(&1));
     }
diff --git a/crates/rrt-runtime/src/inspect/imb.rs b/crates/rrt-runtime/src/inspect/imb.rs
index 0ef63e0..30166ac 100644
--- a/crates/rrt-runtime/src/inspect/imb.rs
+++ b/crates/rrt-runtime/src/inspect/imb.rs
@@ -78,8 +78,7 @@ pub fn inspect_imb_bytes(bytes: &[u8]) -> Result<ImbInspectionReport, Box<dyn st
     let target_screen_width = find_scalar_i64(&entries, "TGATargetScreenWidth");
     let target_screen_height = find_scalar_i64(&entries, "TGATargetScreenHeight");
     let scaleable = find_scalar_i64(&entries, "Scaleable").map(|value| value != 0);
-    let max_percent_of_interface_vram =
-        find_scalar_f64(&entries, "MaxPercentOfInterfaceVRAM");
+    let max_percent_of_interface_vram = find_scalar_f64(&entries, "MaxPercentOfInterfaceVRAM");
     let image_rect = find_i64_quad(&entries, "ImageWH");
 
     Ok(ImbInspectionReport {
diff --git a/docs/rehost-queue.md b/docs/rehost-queue.md
index 5ba2770..2ad8908 100644
--- a/docs/rehost-queue.md
+++ b/docs/rehost-queue.md
@@ -12,7 +12,8 @@ This file is the short active queue for the current runtime and reverse-engineer
 
 - The active static parser head is now the `engine_types` semantics frontier.
   The repo now has structural inspectors for `.car`, `.lco`, `.cgo`, and `.cct`, but the binary side is still only partially semantic: the checked 1.05 corpus grounds `.car` fixed strings at `0x0c / 0x48 / 0x84` plus a second fixed stem slot at `0xa2` and a side-view resource name at `0xc0`, while `.lco` carries a stable primary stem at `0x04` and only conditional companion/body slots at `0x0c` and `0x12` when the leading stem slot is padded.
-  The next honest static work is to keep promoting those fixed lanes into stable parser fields and decide how far `.cgo` and the remaining `EngineTypes` sidecars can be grounded without overclaiming semantics.
+  The checked 1.05 corpus now also splits `.car` auxiliary stems into `126` direct matches, `14` role-neutral roots, and only `5` truly distinct cases, while `.cgo` collapses into five stable scalar ladders instead of arbitrary floats.
+  The next honest static work is to keep promoting those fixed lanes into stable parser fields, explain the five remaining distinct auxiliary-stem cases, and decide how far the `.cgo` ladders and guarded `.lco` companion lanes can be grounded without overclaiming semantics.
   Preserved checked parser detail now lives in [EngineTypes parser semantics](rehost-queue/engine-types-parser-semantics-2026-04-21.md).
   Preserved checked format inventory detail now lives in [RT3 format inventory](rehost-queue/format-inventory-2026-04-21.md).
 
diff --git a/docs/rehost-queue/engine-types-parser-semantics-2026-04-21.md b/docs/rehost-queue/engine-types-parser-semantics-2026-04-21.md
index 9538efe..11a0a68 100644
--- a/docs/rehost-queue/engine-types-parser-semantics-2026-04-21.md
+++ b/docs/rehost-queue/engine-types-parser-semantics-2026-04-21.md
@@ -13,6 +13,16 @@ first `.car` / `.lco` / `.cgo` / `.cct` inspector pass landed.
   - `0xc0`: side-view resource name such as `CarSideView_1.imb`
 - The checked 1.05 corpus (`145` `.car` files) carries all five of those `.car` slots on every
   file inspected so far.
+- The checked 1.05 corpus now also grounds the `0xa2` relation split:
+  - `126` files: `auxiliary_stem == internal_stem`
+  - `14` files: `auxiliary_stem == internal_stem` without a trailing role suffix (`L` / `T`)
+  - `5` files: truly distinct auxiliary stems
+- Those five distinct auxiliary-stem cases are narrow and specific:
+  - `ClassA1T -> ClassA1L`
+  - `CramptonT -> CramptonL`
+  - `WhaleT -> WhaleL`
+  - `classqjl -> qjclassl`
+  - `classqjt -> qjclasst`
 - `.lco` carries one always-present primary stem at `0x04`.
 - `.lco` only carries meaningful secondary slots when that leading stem slot is padded:
   - `0x0c`: conditional companion stem such as `VL80T` or `Zephyr`
@@ -22,6 +32,13 @@ first `.car` / `.lco` / `.cgo` / `.cct` inspector pass landed.
   fixed fields unless the earlier slot is actually zero-padded.
 - `.cgo` looks structurally narrow right now: the checked 1.05 corpus has `37` files, all exactly
   `25` bytes long, each carrying one leading scalar lane plus an inline content stem at `0x04`.
+- The `.cgo` leading scalar is no longer just a loose raw count. The checked 1.05 corpus now
+  collapses into five stable ladders:
+  - `10 -> 20 -> 40 -> 80` across `6` freight-car families
+  - `20 -> 40 -> 80` for `Tanker`
+  - `55 -> 85` for `Auto_Carrier`
+  - `6 -> 13 -> 27 -> 53` for `Passenger`
+  - `7 -> 13 -> 27 -> 53` for `Mail`
 - `.cct` remains the least ambiguous sidecar: current shipped files still look like narrow one-row
   text metadata.
 
@@ -33,6 +50,7 @@ first `.car` / `.lco` / `.cgo` / `.cct` inspector pass landed.
   - internal stem
   - auxiliary stem slot
   - side-view resource name
+  - auxiliary-stem relation counts across the shipped corpus
 - `.lco`
   - full internal stem
   - conditional companion stem slot
@@ -41,14 +59,15 @@ first `.car` / `.lco` / `.cgo` / `.cct` inspector pass landed.
 - `.cgo`
   - leading scalar lane
   - content stem
+  - scalar ladder counts by shared cargo-car family
 - `.cct`
   - tokenized identifier/value row
 
 ## Remaining Static Questions
 
 - `.car`
-  - what the `0xa2` auxiliary stem really represents across locomotive, tender, and freight-car
-    families: alias root, image key, or alternate content stem
+  - what the `0xa2` auxiliary stem really represents in the five remaining distinct cases:
+    alternate content root, paired tender/loco image root, or a narrower foreign-display alias
   - whether the trailing side-view resource can be tied cleanly to `.imb` metadata without
     inventing frontend semantics
 - `.lco`
@@ -57,8 +76,8 @@ first `.car` / `.lco` / `.cgo` / `.cct` inspector pass landed.
   - how much of the early numeric lane block can be promoted from raw `u32/f32` views into stable
     typed semantics without dynamic evidence
 - `.cgo`
-  - whether the leading scalar is enough to justify a named typed field, or whether it should stay
-    a conservative raw scalar until more binary/code correlation exists
+  - whether the leading scalar ladders are enough to justify a named typed field, or whether they
+    should stay conservative report-only ladders until more binary/code correlation exists
 
 ## Next Static Parser Work