card: limitation — score shifts when the answering-model mixture changes (measured)

README.md

@@ -266,6 +266,11 @@ other systems on the independent leaderboard:
 - **Domain coverage.** Scores are meaningful only for the five domains listed. Outside them nothing
   has been measured and no guarantee is published.
 - **Below the surface baseline on disaster and safety.** Stated in the table rather than omitted.
+- **Sensitive to which model wrote the answer.** The probe is fitted on answers from four models.
+  Adding 1,772 answers from a single additional model shifted the mixture and **lowered** the
+  size-weighted score from 0.7278 to 0.7177 — professional exams rose to 0.8575 while every other
+  domain fell. Treat "works on any model's output" as a design goal, not a measured guarantee: if
+  your generator differs sharply from the training mixture, measure before relying on the number.
 - **Revision lock.** The probe is fitted to one specific revision of the base model. Running it on a
   different revision produces **no error and silently wrong scores**; this repository ships the
   matching weights so that failure mode cannot occur.