I have lots of records for sys.dm_db_missing_index_group_stats dating back since the last date the instance was restarted but they have no corresponding record in sys.dm_db_missing_index_groups even though they have current last_user_seek times.
It seems that about every 5 - 15 minutes the recent records are purged from sys.dm_db_missing_index_groups.
Has anyone seen something like this before? What would cause this? Could this be something where an execution plan is not being reused and each compile a different plan is found for the query, one without a missing index?