hi, we don't use proof approvals, so it would be difficult for me to test and confirm that this works; nevertheless, I'm wondering if you've considered an exists statement. Sample code you could use, would look like this:
EXISTS:a:$$OBJCODE=PRFAPL
EXISTS:a:documentVersionID=FIELD:currentVersionID
EXISTS:a:approverID=$$USER.ID
Line 1 = there exists a proof approval
Line 2 = where the proof approval's document version ID is the same as the document's "currentVersionID" (in other words, "hey Workfront, I'm only interested in the latest document version's proofs".
Line 3 [the actual filter] = I went with the filter of "I'm the approver".
You can add any other filter you have built / can build in a regular proof approval report. (e.g. Line 4 -- feel free to filter out some of the approver decisions, or restrict it based on a date... you don't particularly need to figure out the syntax -- just build it in a proof approval report, copy it over, and then append "exists:a:" in front of everything)
I could kind of run a confirmation test in my instance simply by creating a proof approval report and using the same filter, "approverID=$$USER.ID" -- this is because I only had 3 proofs assigned to me, so it was very easy to see that two of the proofs were different versions of the same document. So in my document report, I get two results (two current proofs assigned to me) and in my proof approval report I'll get three results (two current, and one old proof assigned to me)
Hope that helps at least start you in a good direction.