You seem to have two different issues. The main one is that for some reason (which is unrelated to you making a copy of the PDS project file), your source clips have disappeared.
PDS files never store or change any of your original clips, so what could have happened? Did you (or someone else) delete them because you thought you'd finished with them? Are they perhaps on an external drive, or maybe still in the camera/camera's media card?
If you can recover them and/or return them to the original location, both the original and copied PDS project file should work normally.
If you can't recover your original files, you're left with the second problem.
I had a client project with 4 days of shooting to be made into almost 2 dozen videos, and about 2/3 of the way through I $%^#ed up very badly and secure-erased the wrong SSD. In an instant,
all of the PDS files, timeline screenshots and hand-drawn art for
all the projects and various drafts I'd completed up until that point vanished and there was no way to recover any of them.
The good news was that the irreplaceable source clips and all the produced videos were on different drives, but I was in your exact situation when the client needed to make changes to the previously finished videos.
What I came up with was to use the previously produced version as my template, and then extracted, edited and replaced various parts as needed.
For example, if I needed to change or remove a title on a stationary shot, I could use a screenshot without the title and overlay that small section on the existing title to remove it, and then add new text if needed. Basically I focused my edits on the necessary changes and I kept everything else intact.
The specifics of what will be needed on your end will be completely dependent on what kind of footage you've got and what kinds of changes you're wanting to make. Some kinds of changes may not be possible, like zooming out on a clip that you'd originally zoomed in on too much in on, or extending the length a scene because you no longer have access to the original clips.
However, most of the existing content in your original produced video will probably still be usable for your Rev 2 project.