Doesn't help with the 10 point difference. Woe.

Xenthos probably has a pre-tempering plate.
From the (fairly abundant) forging tries that I did after tempering was introduced, I'm fairly positive that you cannot get better armour than 180 points total (before master armour and runes) any more, neither with tempering (obviously) nor forging.
So all those old-schoolers with their super plates better hold onto them. I really regretted not putting more time into forging a good plate before tempering got introduced, I got a 92/90 fairly quickly, so something better would probably have been realistically possible.

Those do not exist anymore. All pre-tempering plates were removed from the game. (I miss my 107/107 BASE plate, Melan at one point forged a 105/103ish one after like a RL month of forging, too, which wasn't one of the bug fix 107's from 6 years ago.)

I had my 92/90 until I scrapped it (quite a while after tempering got introduced). Not exactly over the top like the ones you mentioned, but still not achievable any more, to my knowledge.

I have a 91/92 sitting around somewhere, glad I haven't scrapped it. I had thought to try for a more thematic appropriate plate the "old way", but if what people are saying is true, I won't waste my time.

Now, if they came down and said "we're gonna make all your plates 180 sum maximum", I certainly wouldn't complain either, so long as all plates got the same treatment.

That, and two handed hammer spec!

Mine still exists... it has 182 base stats.

That's pretty much why I haven't touched it.

Yours also wasn't one of the uber pre-tempering plates. Anyhow, I'd bet you can still forge 182 total eventually.

I tried for a fairly long time (not excessively long, but a few rl days, I think) and also recorded max stats. Before the change, I had got cutting or blunt stats of 104 fairly often, not any more. Before that, I had got a helmet and a plate with more than 180 total rather quickly (plate took a few hours max), not any more. If someone feels inclined to try again and more often, it would be interesting to know if they get the same result. I could have been very unlucky, but I have my doubts.