Clarify firing of import_notification_stream in doc comment

substrate/client/api/src/client.rs

@@ -65,9 +65,15 @@ pub trait BlockOf {
 pub trait BlockchainEvents<Block: BlockT> {
 	/// Get block import event stream.
 	///
-	/// Not guaranteed to be fired for every imported block, only fired when the node
-	/// has synced to the tip or there is a re-org. Use `every_import_notification_stream()`
+	/// Not guaranteed to be fired for every imported block. Use `every_import_notification_stream()`
 	/// if you want a notification of every imported block regardless.
+	///
+	/// This notification stream is fired...
+	/// - During initial sync process: if there is a re-org while importing blocks. See
+	/// [here](https://github.com/paritytech/substrate/pull/7118#issuecomment-694091901) for the
+	/// rationale behind this.
+	/// - After initial sync process: on every imported block, regardless of whether it is
+	/// the new best block or not, causes a re-org or not.
 	fn import_notification_stream(&self) -> ImportNotifications<Block>;
 
 	/// Get a stream of every imported block.