I own several underworks 997s. Awhile back I bought a brand spankin' new one in a medium. I had been wearing larges because I was a large and eventually got enough to get a medium since I lost weight. I had an old medium (I was originally in between sizes) and it's pretty stretched out but feels tighter than the new medium I just got. They seem roughly the same size, even with the old one being stretched out. I think I might've realized what the big sizing difference was.

The old one was the pre "something% longer" type of 997s. It sits at the top of my butt while the new one can stretch to my thighs. I think there might've been a difference either in sizing or material in these two versions.

I really kinda wish I had one from before the 'whatever inches longer' change- mine went WAYYYY too far down before I cut it. I don't  know why anyone would need that extra length, it's far too much than needed to tuck it into pants.

It also seems to be wider or has more give than the older one.

The first time I checked my size, I don't know if it was before or after the change, but I measured as a small. Now I'm wishing I had an XS- the small has too much give. Gonna get one when I have more money.