I’ve not seen the aforementioned Charlie post but “proof copies” sounds like a fancy way of saying “extras”. Last year (or perhaps 2019) an Art Academy Kyogre EX appeared for sale from a well-known eBay seller who also had a load of other Art Academy cards for sale, however the winner of the Kyogre EX supposedly still had all 100 of their cards at the time so it was believed that this card along with all of their other Art Academy cards were extra copies which had left the factory at the time of printing.
Extra copies are known to exist for quite a lot of low-distribution cards including the Illustrator. The recently-shilled $130,000 PSA 9 SSB No. 2 Trainer card is also part of a known set of graded extra copy trophy cards and the majority of the cards from the 2010 Design Contest which have surfaced are also thought to be extra copies.
Until the first Kyogre EX sale the Art Academy set was not known to have any extra copies in circulation but now we’re at a point where 13 of those have been graded and several of them have been from the same seller as the first copy. I don’t know however how many of the original stack of 100 the winner still has or if all 13 of those are simply extras
You may be interested in a post I wrote recently going over some charts I put together comparing the PSA populations of the Art Academy, 2010 and 2009 Design Contest sets which all had an official 100 cards awarded to the winner distribution: www.elitefourum.com/t/the-pwcc-megathread/18812/3753.
Another thread you may be interested is the Analysis of the Extra Trophy Cards that have surfaced so far.