Year the car was first tagged, or model year. There are no real 1976 914's. They are all left over 75's. Most 912E's appear to have been made in 75 also. But in the eyes of CA DMV, they are 1976's.

Whatever is on the title, which is also in the DMV computer, is what counts. Doesn't matter what the car says on it.

If you want to try it, I've certainly heard of people managing to convince the DMV their car was titled as the wrong year initially and getting a new title to match the year of manufacture, if there's a plate on the car that says it was made in an earlier year, or you can provide some other documentation. I'm sure this requires a great deal of persuasion and guile to make happen, or a particularly stupid (or pliable) DMV employee, or both.