diff --git a/.crow/weekly-rebuild-missing.yaml b/.crow/weekly-rebuild-missing.yaml
index 5afb3c3..a12676d 100644
--- a/.crow/weekly-rebuild-missing.yaml
+++ b/.crow/weekly-rebuild-missing.yaml
@@ -9,6 +9,12 @@
 #             single <os>-<arch> to run just one.
 # Arch placement is handled by the group label (rpkgs-amd64, rpkgs-arm64).
 #
+# 9 OS versions x 2 arches x 3 shards = 54 rows. Crow counts the *declared*
+# matrix against CROW_MAX_MATRIX_SIZE before any `when:` gate is applied, so a
+# single-slot manual run expands all 54 too. The server default is 50 and was
+# raised for this; `crow lint` does not check the limit, so adding an OS
+# version here is only caught when a pipeline is triggered.
+#
 # The shard picks up its own slice and re-derives what is still outstanding
 # from the bucket, so a restart resumes rather than replaying; see
 # local/rebuild-missing.R.