E121-80 Back "Types" Question

[VoodooChild]

Does anybody know why the four different E121-80 Back "Types" are not more universally accepted? I know that Rhett wrote a 2011 Old Cardboard article on the subject, but that is the only reference I can find. I've never seen a TPG flip which designates any sort of Type for E121-80 like I see with other issues (E210 and V61 come to mind among many others) and no Ebay or AH description ever mentions them. Does it have to do with the ACC not classifying the different types? If so, does the ACC ever get amended/updated when new info is discovered? Do any of you Type Collectors try and get the four different "Types" for your collection? Are there many other issues out there who's "Types" are not accounted for in the ACC and are not widely accepted?

Here's my four different types. The differences are subtle and maybe that has something to do with my question, but I've seen other issues with subtle differences in the various Types which are universally accepted: