What do you do in this situation? After the proof has been approved, further down into the project someone indicates they need to make edits to the proof.

I work in a creative design group and there are times when we get almost all the way through a project and the owner of the piece updates to say, oops, I found another change that needs to be made on the proof. The project tasks are all marked 100% through most of the project and now we need to backtrack or get the proof back to the proof owner and revisit all of the tasks that we've just been through. We have a way of handling it now, but I wonder how other groups handle this scenario? You know it happens, just don't know how to properly handle - thanks!