Filter by Proof Copies

Am I missing something?

My workflow is primarily to digital, but now I'm printing more. When I have to print, the workflow is as follows:

1. Select candidates from images that have already been processed.
2. Turn on soft-proofing and create a proof copy (because I do not want to alter my digital-ready "original").
3. Edit the proof copy, send to print.

My problem is that I now have a library filled with edited images for both print and digital. 

It would be really useful to then be able to filter (in or out) the "proof copies". 

I currently filter by edited images and my rating to find the images I want. But now my proof copies are in the mix as well.

I know that there is a virtual copies filter, but I often make several virtual copies of the same image when working on different looks or crops. So that doesn't do the trick.

Is there a way to filter by proof copies? Or do I have to label them all as I make them?