diff --git a/skills/lemonade-router-builder/SKILL.md b/skills/lemonade-router-builder/SKILL.md
index c5f094a..cb32839 100644
--- a/skills/lemonade-router-builder/SKILL.md
+++ b/skills/lemonade-router-builder/SKILL.md
@@ -237,6 +237,13 @@ The `x-lemonade-route` response header carries the matched rule id (or
 `x_lemonade_route`: `{ route_to, matched_rule, default_used, outputs,
 trace[] }` - useful for verifying each rule fires as expected.
 
+**Read `default_used`, not the rationale.** A fallback returns HTTP 200 with no
+error, so the silent failure Step 4 warns about is invisible unless you check
+the trace. `"default_used": true` with `"matched_rule": ""` is the signature.
+In Mode A an empty `rationale` on its own is *not* a fallback signal - a
+successful route to a non-first candidate commonly returns one. See
+[reference.md](reference.md#reading-a-mode-a-trace).
+
 ## Defaults summary
 
 | Field | Default when the user doesn't say |
diff --git a/skills/lemonade-router-builder/examples.md b/skills/lemonade-router-builder/examples.md
index 9bdc050..ceb2c21 100644
--- a/skills/lemonade-router-builder/examples.md
+++ b/skills/lemonade-router-builder/examples.md
@@ -7,6 +7,19 @@ should produce. Note what was defaulted: names, ids, thresholds, `on_error`,
 is derived from the default candidate rather than a fixed literal, so the
 examples below each get a distinct name.
 
+**These are shape references, not runnable policies.** Each names models a
+given host may not have. They all pass `scripts/validate.py`, which
+deliberately cannot check model existence - that needs a live server. Register
+one against a host missing a referenced model and the server rejects it:
+
+```
+400 Collection component not registered: '<model>'.
+    Pull or register it before referencing it in a collection.
+```
+
+That is correct, documented behaviour. Substitute models the target host
+actually has (`GET /api/v1/models`) before registering.
+
 
 ## 1. Pure intent, no concrete signals → LLM-as-router
 
diff --git a/skills/lemonade-router-builder/reference.md b/skills/lemonade-router-builder/reference.md
index 6bf2ece..1a59aaa 100644
--- a/skills/lemonade-router-builder/reference.md
+++ b/skills/lemonade-router-builder/reference.md
@@ -190,6 +190,29 @@ for keyword/metadata conditions. Registration errors come back as descriptive
 parser messages (e.g. `routing.default_model 'X' must be listed in
 routing.candidates`); fix the field it names and re-POST.
 
+### Reading a Mode A trace
+
+Mode A has no author-supplied rule ids, so `matched_rule` reports synthetic
+ones - `__route_0`, `__route_1`, ... - one per entry in `routing.candidates`,
+in declaration order.
+
+Two things about these traces are easy to misread. Observed at 11.5.2:
+
+- **An empty `rationale` is not a failure signal.** Routing to a candidate
+  other than the first commonly returns `"rationale": ""` and `"score": 0.0`
+  on a perfectly successful decision.
+- **Fallback has one unambiguous signature** - all three together:
+
+  ```json
+  { "default_used": true, "matched_rule": "", "rationale": "", "score": 0.0 }
+  ```
+
+  with `x-lemonade-route: default`. Check `default_used`, not the rationale.
+
+A fallback returns HTTP 200 with no error field, so a policy that falls back on
+every single request is indistinguishable from a working one unless you ask for
+the trace.
+
 ## Desktop-editor compatibility
 
 Users may open the generated policy in the Lemonade desktop app's Hybrid