I realize this post is about six weeks old so you may have found a solution. However, I was wondering if the problem has (had) something to do with Tableau's need to link both state and county in order to uniquely identify a county. I understand that you have some actual "missing data" for some counties but your issue seems to be more fundamental. Since the TDE format uses columnar data formats maybe it's an indexing issue with "state" and "county" pairs. I may be way off (won't be the first time), but it would be nice to have unique US county identifiers like FIPS codes built into the geographic roles.