Just a giant write-up I made to explain the differences between files, in case some users were curious. I hope this clears up the confusion around why some duplicates are allowed and others aren't.
I'm looking to make this more user-friendly to read, but I avoided writing it in Dtext because I'm used to Markdown a LOT more (it allows me to edit much faster).
With all that said, I'll just post the link here to anyone that wants to read it. That Github account is my personal dupe, by the way -- you'll be seeing it more when I publish more danbooru-related things.
Updated by Mikaeri