I agree with Chris.
As a reference, here is a Mk1, model years 1976-1981:
Here is Mk2, model years 1982-1985:
Here is a Mk3, model years 1986-end:
All the above are/were mine.
Remember, model years usually started in September of the previous year.
As Chris said, every model year changed (fairly significantly, especially 1977-1986). I have a little guide I made myself at home with some of the changes to identify which model year is which, I'll paste it here later.