The steaming tip was great! Got the label off, no problem.
Then I put a straight edge on the stone, and it's warped. I'm partway through the flattening, on 80 grit sandpaper sprinkled with 60 grit SiC. It's some work, but the reward beckons.
Ah good to hear! Yeah - I do it on pretty much every labelled stone, and usually keep them in little baggies so I can use stuff with worrying. You can do it with even quite delicate labels, but yours there was in such good condition that I was pretty confident it'd steam off with no trouble at all.
Looks like it'll be an absolute gem once fully flat .