I've been staring at this one for a while.
It's as terminal as a die state gets, a real surprise to see dies age this greatly without cracking, on this issue. Not unprecedented, though. I don't have access to the full variety listing for these, but in research I saw at least GR-20 aging to this state with no cracking. GR-21 looks like a strong candidate when one looks at how the date might wear into a really advanced die state; yours has a rather odd look.
I can't say for sure it's authentic, but it's hard to imagine counterfeit dies this aged. So I'm assuming it's real and trying to figure out how it came to this.