I don't see why that would be the case. If there are outstanding bugs in 7.0, you won't need anything from 6.0 to reference them, they would stand on their own, would they not? If something clips or has a hole in it or is overly pixelated or the hair stands very far off the head model etc., you wouldn't need earlier reference photos to point it out.
Though certainly take screenshots if you want to preserve a memory.
