my point was: You can't count the LEGO man as a determinant for ABS floating, if you want to do that use a LEGO brick not a figurine that encloses air afair at least in chest and head.
The slippery feel of POM -I think I even got that from your wikis, and as soon as I laid my hands on POM for the first time I knew what was meant, the difference is obvious and its also different from worn ABS and such.
As for the Stems and shrinking, this isn't meant to be a final indicator, but maybe its's a hint, and these are crappy cellphone pics:
Cherry OEM caps here - Raptor K1 on the left vs G80-1502 on the right, both are POM.
Cherry also seems to not mark POM caps on the inside (OEM caps) - this is a PBT only featrure (as for my experience).