The whole thing is too confusing for me. I feel like going down there and having a sit down with the lady at the window. I'll have to say, she was very nice AND attractive. The owner had everything current through 2012, but he wasn't charged tenencia They were collecting for 2013, but only for "derechos' had he been registering for himself. He gave us that part, but due to my wife being charged tenencia, she put the process off till she has her IFE.
It might be interesting to ask TJ how his car purchase was treated, since he recently bought a Mexican plated car and he isn't a Mexican citizen.
That car is a 2007, so his tenencia wouldn't be too much, I suppose, if it turns out he has to pay it the next time the registration renews: on a newer car, mine runs just about 4,000 pesos for all fees, each year, including the tenencia.