I started with Logic 9, so my updates are not far in between, but I used to be a Logic/PC user. I have the current version but I could still boot up Logic 9 if I wanted to. I think a lot of strange things would happen if I updated from earlier versions, like say 6 or 7. But see, this was what I was saying: When you download the update, you are dowloading the whole program. So that when you install the new version you are still left with the old. For safety reasons, I do not delete the old versions.
The only problem I have are the IR files. I've compiled other IR files but I want the original ones for comparison, among other things.