Hey Don! New member, been a fan of the site for a while.
I had some info on the Claw from Lev Gleason. You wrote that no explanation was ever offerred. According to Jeff Rovin's ENCYCLOPEDIA OF SUPER VILLAINS, The Claw is actually the offspring of an Asian brute named Mei Ting and a Caucasian mutant woman (with fangs, partially explaining the Claw's appearance) named Zora. Essentially, Mei Ting was muscling in on Zora's restaurant (Rovin says she was the literal boss from hell, killing employees who requested payment). He pulled Zora's veil off in the ensuing struggle, exposing her fangs. She decides to marry Mei Ting in order to keep her secret. Months later, the two were seen jumping off a cliff to their deaths, and the villagers found the Claw as an infant at their abandoned house. He was then taken to a private school ("and woe befall the teacher who failed to give him the highest mark"), and then to a prison, where his size changing powers first manifested.
Perhaps this was kinda superfluous (didn't realize how long that history took until I typed it!), but I just thought you'd like to know :) Keep up the good work!