I think I've spotted the difference...

[Nygeel]

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.

[CursedFireDean]

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.

[Nygeel]

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

[CursedFireDean]

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.