diff --git a/cylc/flow/broadcast_mgr.py b/cylc/flow/broadcast_mgr.py
index 2bbb1d7c273..c615e88be82 100644
--- a/cylc/flow/broadcast_mgr.py
+++ b/cylc/flow/broadcast_mgr.py
@@ -202,6 +202,17 @@ def load_db_broadcast_states(self, row_idx, row):
             "key": key,
             "value": value})
 
+    # BACK COMPAT: post_load_db_coerce
+    # The DB at 8.0.x stores Interval values as neither ISO8601 duration
+    # string or DurationFloat. This has been fixed at 8.1.0.
+    # url:
+    #     https://github.com/cylc/cylc-flow/pull/5138
+    # from:
+    #    8.0.x
+    # to:
+    #    8.1.x
+    # remove at:
+    #    8.x
     def post_load_db_coerce(self):
         """Coerce DB loaded values to config objects, i.e. DurationFloat."""
         for namespaces in self.broadcasts.values():
diff --git a/cylc/flow/parsec/validate.py b/cylc/flow/parsec/validate.py
index b1226071b23..70bde7678bb 100644
--- a/cylc/flow/parsec/validate.py
+++ b/cylc/flow/parsec/validate.py
@@ -1045,7 +1045,7 @@ def _coerce_type(cls, value):
         return val
 
 
-# BACK COMPAT: post_load_db_coerce
+# BACK COMPAT: BroadcastConfigValidator
 # The DB at 8.0.x stores Interval values as neither ISO8601 duration
 # string or DurationFloat. This has been fixed at 8.1.0, and
 # the following class acts as a bridge between fixed and broken.