Use this query to find where users have their post migrated but they never followed the question to the target site.
Q&A about the site for members of the workforce navigating the professional setting
SELECT OwnerDisplayName, Posts.Id AS [Post Link] , PostHistory.CreationDate AS [Migration Date] , Posts.CreationDate AS [Post Date] FROM Posts JOIN PostHistory ON Posts.Id = PostHistory.PostId WHERE PostHistory.PostHistoryTypeId = 36 AND Posts.PostTypeId = 1 AND OwnerUserId IS NULL ORDER BY Posts.CreationDate DESC