Yes, it points out user #s which have posts.
So you'd most likely want to recreate a user with that number. Or find the posts with the B_PosterId of that number, set the B_PosterId to 1 and B_Reged = n for that post.
Otherwise posts for any missing users won't appear, as when it tires to join the usernumber in the pOsts table to the users table, it fails, thus typically the whole thread won't appear, even though it exists in the database.