it’s a nominal measurement, but i personally find a 25% variance to be unacceptable for consistency. if it was .23 to .27, that’s one thing. but if it can be 25% off, then that’s .2 to .3 range, which is huge when it comes to any kind of joinery.
and in plywood, it’s a bigger issue because you can’t sand it thinner if it’s over like you could with hardwood.
JPPlus sells finished maple/walnut/etc plywood that’s identical to Proofgrade other than being cut to 12x24" instead of 12x20" per sheet. It’s always been the same color, finish and thickness for me over the years. I would buy Proofgrade when I had referral credits, or Laserbits otherwise for the lower price (there’s always a 15% off coupon for that site too).
Anyway, the reason I mention that is they advertise their sizes as 1/8" and 0.205". I think that’s the actual size Thick Proofgrade is intended to be. They may even be coming from the same manufacturer.
and that’s also probably the reason they call them “medium” and “thick” instead of .125 and .25.
i have very little thick PG (never bought it separately, just what came with the machine) and the medium has always been way closer to .125 than that difference in thick. i don’t know if i remember .125 being under .12 for me, so w/in .005, not w/in .05, which is a huge difference.