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 9fbe82f0..fd6888ef 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
@@ -82,3 +82,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
   `state` under the local name `<name>-old` bound to its existing bucket, read through `stdio.State` like any section,
   copied once by A-8's rule (a key only where the template lacks it), and retired with §613's other old sections.
   The developer says which of the two the runtime allows, with the line of code that shows it.
+- **A-21** (§518, §345, §457, §643; principles 7 and 3) Each put-chunk and each get call carries `objects`, the store's
+  local name, as today's put does. The chunk is a constant of `buscalls`, 512 KiB, which fits under the bus's default
+  maximum payload of 1 MiB whatever the bus is set to; a value larger than one chunk goes by session, a smaller one in
+  one call as today, so there is one threshold.