Personally I just ignore them(Raising Steam and Snuff). There are too many inconsistencies with how Vimes and Lipwig are characterized in those books, that I can't see them as the same characters. I haven't started the Shepherd's Crown for the same reason.

I don't think that any fan of his is under any illusion that those books are up to his standard, but he has so many good books that his legacy will be safe.