Sure, and history is full of authors who died 95% of the way through a book, etc, having their work completed by a relative or someone hired by the publisher, spurring raging debates over author's intent, etc.
I hate to get all post-modernist on this thread, but the whole idea of authorship in art is much less relevant than people give it credit for. The meaning of a work to society is frequently not what the author or authors or executive producers or publishers intended it to be. And who's right when there's a disagreement between the creator and society? IMO the readers, viewers, fans, etc, are always right. It's society who gives a work its real meaning, which is how the meaning of a work can change over time, and successfully become timeless... or fail to do so.
So it doesn't MATTER who edited what when and for what reason, really. What matters is that a big chunk of society saw this hodgepodge collective work and fell in love, probably for hundreds of completely different reasons. And it became a cultural force of its own at that point.
And that's what's important, the cultural impact, and that's what we're trying to preserve. All the discussion about author's intent and definitive versions and crap is beside the point. Not that we can't have opinions on those, naturally.