The libraries are on your original installer discs.
It is always a good idea to keep copies of the old libraries on your hard drive for this reason. There has been much discussion of library management so a search of ArchiGuide should provide you with lots to read about this.
Another good practice is to save the project as an archive (.pla file type) when the project is completed. We have also done this with older projects that we have converted to 8.1 so we don't have to endure loading all those old libraries.
I'm not sure what you mean by revision, or at least why it would be a problem. I recommend that you bring all your projects into 8.1 the way I described, and add only new (8.1 or third party) library parts, keeping only the older ones you already used from the previous libraries.