diff --git a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
index 18a2d134..cadf1049 100644
--- a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
+++ b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
@@ -643,3 +643,6 @@ names the principle that settles it, and is cited as "design 47 G A-n".
   its kind is in its body only, as §600 says. A build seat definition's `stream` names only the queue, and the
   generated accept subjects follow; the kind in the subject goes. §543's main subject takes `build` and `run` as
   written, the checker's asks riding it until it goes.
+- **A-171** (§579, A-169; principles 2 and 8) The `pinned` event's `catalog` entries name their branch: each is
+  `{branch, revision}`, in the mesh-delivery seat's definition and from the gate that says it, so a holder keys the
+  pin `<branch>.<revision>` from what the event says.