diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 2b323c0272..83993cb969 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -589,8 +589,13 @@ def _clear_out_of_date_sliding_sync_tables(
     `sliding_sync_joined_rooms`/`sliding_sync_membership_snapshots` tables.
 
     This accounts for when someone downgrades their Synapse version and then upgrades it
-    again. This will ensure that we don't have any out-of-date data in the
-    `sliding_sync_joined_rooms`/`sliding_sync_membership_snapshots` tables.
+    again. This will ensure that we don't have any out-of-date/stale data in the
+    `sliding_sync_joined_rooms`/`sliding_sync_membership_snapshots` tables since any new
+    events sent in rooms would have also needed to be written to the sliding sync
+    tables. For example a new event needs to bump `event_stream_ordering` in
+    `sliding_sync_joined_rooms` table or some state in the room changing (like the room
+    name). Or another example of someone's membership changing in a room affecting
+    `sliding_sync_membership_snapshots`.
 
     FIXME: This can be removed once we bump `SCHEMA_COMPAT_VERSION` and run the
     foreground update for
@@ -609,8 +614,11 @@ def _clear_out_of_date_sliding_sync_joined_rooms_table(
     Clears out-of-date entries from the `sliding_sync_joined_rooms` table.
 
     This accounts for when someone downgrades their Synapse version and then upgrades it
-    again. This will ensure that we don't have any out-of-date data in the
-    `sliding_sync_joined_rooms` table.
+    again. This will ensure that we don't have any out-of-date/stale data in the
+    `sliding_sync_joined_rooms` table since any new events sent in rooms would have also
+    needed to be written to the `sliding_sync_joined_rooms` table or some state in the
+    room changing (like the room name). For example a new event needs to bump
+    `event_stream_ordering` in `sliding_sync_joined_rooms`.
 
     FIXME: This can be removed once we bump `SCHEMA_COMPAT_VERSION` and run the
     foreground update for
@@ -672,8 +680,10 @@ def _clear_out_of_date_sliding_sync_membership_snapshots_table(
     Clears out-of-date entries from the `sliding_sync_membership_snapshots` table.
 
     This accounts for when someone downgrades their Synapse version and then upgrades it
-    again. This will ensure that we don't have any out-of-date data in the
-    `sliding_sync_membership_snapshots` table.
+    again. This will ensure that we don't have any out-of-date/stale data in the
+    `sliding_sync_membership_snapshots` table since any new membership changes in rooms
+    would have also needed to be written to the `sliding_sync_membership_snapshots`
+    table.
 
     FIXME: This can be removed once we bump `SCHEMA_COMPAT_VERSION` and run the
     foreground update for