I agree with the max of two years and that it is only allowed in the last year.
There seems to be two things here, timing of the extension under CV, and the length of the extension
Timing: I vote last year only. Realistically, if you are a player, why would you sign a new contract coming after a down year if you existing still has not expired?
Length: I am for the stipulation where the total length of existing contract and the new contract is less than or equal to current contract length restrictions, e.g, 5years for
extensions that are more than 10M, 4 years for
extensions greater than 5.5M but less than 10M.