diff --git a/docs/nips/NIP-CL.md b/docs/nips/NIP-CL.md
index a88ab43977..222bfb9e0d 100644
--- a/docs/nips/NIP-CL.md
+++ b/docs/nips/NIP-CL.md
@@ -116,6 +116,25 @@ The relay MUST match `#t` and `#P` before it applies `limit`, as NIP-01
 requires. A relay that reads the newest channel events first and matches tags
 after can return a short or empty page while matching channels exist.
 
+## Choosing one channel
+
+The relay does not make labels unique. Many channels can share a label, and
+any owner or admin can set any label. So two creates for the same label can
+both succeed, for example when two processes of one agent start at the same
+time.
+
+A client that needs one channel per creator and label:
+
+1. queries `{"kinds": [39000], "#P": ["<creator>"], "#t": ["<label>"]}`;
+2. creates the channel only if the query returns nothing; and
+3. when the query returns more than one channel, uses the oldest one.
+
+The oldest channel has the lowest `created_at` tag value. If two channels have
+the same value, the lowest channel ID (`d` tag, compared as a string) wins. A
+channel without a `created_at` tag ranks after every channel that has one.
+Every reader that follows this rule picks the same channel, even after either
+channel is edited.
+
 ## Trust
 
 A client that relies on these tags MUST check that the relay's key signed the