See what you can do with a proof approval report. You may not be able to get clean %s like you're after but you can at least filter in all proofs from X timeframe and add a column for proof progress to see if it was sent, sent > opened, etc. I tried to see if you could group it by progress for a chart by progress but not happening bc there are multiple possibilities for the proof progress.
You can sort the report by this column to split out sent vs. sent and opened and other progress stages and deduce a percent that way to see # of certain stages vs. # of proofs you're pulling in.
If this helped you, please mark correct to help others : )