If you don't set the ground rules for the engagement this year, you will regret it.
Personally, I would tell the client that it is not your practice to produce incorrect tax returns, that it is his choice to correct the prior years, but if he does not, you cannot produce a correct return this year because the carryforwards are incorrect and you will not sign a return you know to be wrong. Make him make the choice to stay or go.
Tom
Longview, TX