tree changes had already

1 files changed, 3 insertions, 1 deletions

diff --git a/docs/peers.md b/docs/peers.md
index 59b45d0..939f318 100644
--- a/docs/peers.md
+++ b/docs/peers.md
@@ -316,7 +316,9 @@ cycles; taking only one it reaches routes around links that don't work: where a
 behind NAT reaches a single member, that one comes first among those as far from it,
 and the others take it as their parent. A sync message that passes a
 writer's change on says whose; whoever applies one sends it at once to its children in
-that writer's tree, however it got it. Its announcement round then goes only to the
+that writer's tree, however it got it. So does one that had the change already: it may
+have come another way first without saying whose (with an answer to one of its own
+messages, say), and then nothing was passed on. Its announcement round then goes only to the
 neighbours the tree leaves out (no member they reach comes before them, or the member
 list's graph doesn't have them); all others are told in a slow round 2 s later, which
 catches what a tree missed (a parent that went away, nodes whose views of the tree