Triplex With only two Units Recognized by County

[Christian Daviscourt]

As the title states, I am interested in a triplex (converted single family home) but after talking with the realtor only two of the three units are recognized by the county. With that said, is it really just a duplex they're selling and trying to spin if off as a triplex? All three units are occupied, but I could see there being legal issues with the one not recognized by the county. 

Could someone please shed some light on the "not recognized by the county" bit. Should I run away from this deal. The potential cash flow is pretty stellar otherwise.