Yeah I don’t know for sure if it changed for ‘72 or ‘73. But I know for sure that from ‘73+ the fillers went through from the outside. Might have started in ‘72 going off of the older picture laying out the ID’s of the caps.
The caps are a pain, some of the changes were relatively minor and I think the parts cross-references are all over the map as far as what’s supposed to fit what. Add that to the fact that a really small difference in a tab can mean it doesn’t fit tightly and buying a cap off the internet to fit your car is a total crap shoot. They’re listed incorrectly all the time, and then they’re all made overseas now so even if you get the right one it doesn’t necessarily mean it’ll fit right anyway.