These particular accounts do NOT exist in any groups, whether local or in Active Directory. However, they are AD accounts that have been disabled. Now I am wondering if SQL Server is somehow resolving the SID with the AD account itself. I just ran SUSER_SNAME for one of the SIDs in a query against all 60+ instances that range from SQL 2000 to 2012. Guess what? The same SID returns the same account on every single instance.