When I have sold a tank in the past, the tank that replaces it in the garage is the T1E6. I presume because it was the first tank in the list. I no longer have the T1. I just sold a tank and the tank that replaced it in the garage is the T26E5. To my knowledge, I've never had that tank. Maybe it was a rental under some event? Regardless, I played with the filters to see if I could get it to show up again after I switched to a different tank. It is not to be found. I sold another tank a little later and there it was again. I threw a 50% crew into it just to see if it would go into battle. It did.
I couldn't do that again in 5 tries with a good crew and actual consumables...