The T412 took over from the T411 in 1972, but production ended in 1974. They just didn't sell, and eventually other models took over like the Golf. The T412 was really just a T411 with a face lift. The main difference was at the front where it had more angular lights.
For more information on the type 4 see type4.org and Toms Type 4 Corner.
See also T411 and Type 4 engine.