OK, going on the assumption that the Godfather canon includes:

The Godfather (novel)
The Godfather (film)
The Godfather, Part II
The Godfather, Part III

Say FFC made a Part IV without Puzo (obviously). Would you consider it canon?

What if a different director made a Part IV? Canon?

What if FFC made the Returns and Revenge novels into movies? Canon?

What if a different director made Returns and Revenge? Canon?

Basically, is the Godfather canon dead?