Sounds like your client prepared his own taxes, not that it changes anything. As I'm sure you are aware that you only have to file this years taxes correctly, and point out the error to client. He will decide if he is going to correct the errors. Don't know if this is correct, but if it were me I would amend the 1065 that ended the partnership, and mark it as final. I would then amend the 1040 for the incorrect years, by adding a schedule C and removing the K1 on 1040X, and explain the change. Just my 2 cents. 😁