expiry with increment

DOC-11523

modules/howtos/pages/kv-operations.adoc

@@ -173,6 +173,8 @@ Values above 0ms but below 1000ms are rounded up to one second before being sent
 
 The value of a document can be increased or decreased atomically using `Binary.Increment()` and `Binary.Decrement()`.
 
+NOTE: Increment & Decrement are considered part of the ‘binary’ API and as such may still be subject to change
+
 .Increment
 [source,csharp]
 ----
@@ -197,8 +199,7 @@ include::example$KvOperations.csx[tag=binarydecrement,indent=0]
 include::example$KvOperations.csx[tag=binarydecrementwithoptions,indent=0]
 ----
 
-NOTE: Increment & Decrement are considered part of the ‘binary’ API and as such may still be subject to change
-
+TIP: Setting the document expiry time only works when a document is created, and it is not possible to update the expiry time of an existing counter document with the Increment method -- to do this during an increment, use with the `Touch()` method.
 
 include::{version-common}@sdk:shared:partial$atomic.adoc[tag=xdcr]