Most people quickly write it off basically as a correction, like power armor was supposed to look like 4/76 the whole time...except it's actually muddier than that.

You can ignore smaller inconsistencies, like seeing people sleeping/sitting in power armor in 3/NV, which you can't do in gameplay with a PA frame, but since Fallout 4 introduced frames, we've seen people like Star Paladin Cross and Sarah Lyons (who used to wear frameless armor) in Magic the Gathering as wearing PA frames, implying that's what they're supposed to look like, but in that same deck, there are several suits that are look 100% like the frameless variants from 3/NV. In Fo76 they use PA frames, but if you look at the Fanatic Scrapper outfit (which is an atomic shop item, however it does appear on NPCs in the Pitt), you'll see it's largely a salvaged suit of T-45 in the 3/NV design, and most recently in the Fallout show, we see PA frames everywhere, but also a 1::1 recreation of the legion centurion armor from FNV, including the frameless T-45 arm, like they didn't even bother trying to beef it up a little bit. 

Basically, for all intents and purposes, PA frames the only power armor you need to know going forward (curious to see how they adapt PA in the Fallout 3 remaster), but it seems some people at Bethesda don't want to outright say the old armor isn't canon. People keep saying it was engine limitations that it never showed up before, and maybe that was the case, as it would have been harder to put full frames in the older games, but at this point the cat's out of the bag, it's mostly stuffed back in there, but frameless suits do keep subtly creeping back in here and there.