I’ve cracked and regraded dozens of 8.5’s. I wrote a quick article about it. It is an abomination of a grade. None of the cards that I cracked and regraded earned a 8.5 the second time around.
www.elitefourum.com/t/psa-8-5-grading-anomaly-december-2016-january-2017/18738/1
More background if you care for a longer read. Basically there was a short stint where PSA was handing out 8.5’s at a historical rate in late 2016 to early 2017. Every PSA 8.5 that went back on the second time around achieved an 8 9 or 10. I’ve regraded more since but haven’t kept great data. Most have gone to 9’s the second time around and I have still yet to have an 8.5 crack and regrade back to an 8.5.