Just to share a nasty surprise.  I was using Query Builder to count the number of visits that had dates present  The generated code was
(SUM(t1.SGVisitDate>.)) AS CHEvisitDone
When that code runs against a SAS dataset, all is well.  When it runs against an Access table via a LIBNAME (to ACCESS, not to ODBC), it returns all NULLS (no errors or warnings).
If I change the summary function to 
COUNT(t1.SGVisitDate) AS CHEvisitDone
I get the expected answer with either source.
Caveat emptor!  I will also send to tech support.