I am marginally suprised this thread ended as quietly as it did.
The weight of my ~1969 avacado (22) is noticeably heavier than my 1995 (green) or 1999(red) Mastertouch lids. And those MT's include thermo hardware, and do not have massive porcelain chips that the avacado does. The old lid also seemed to retain heat longer, although that is anecdotal.
My daughter was helping me cook on them yesterday, and she noted the old one was heavier independantly.
Did ed ever get the micrometer out to measure the actual lid thickness?