FWIW, I do think they might have changed things very recently--but only for some legal argument (maybe as a result of Corellium...) as opposed to any technical

FWIW, I do think they might have changed things very recently--but only for some legal argument (maybe as a result of Corellium...) as opposed to any technical one--but they really did just leave every single variant of every single update on their server... I even made a tool for jailbroken iOS devices that would get the original update files from Apple's servers and implemented exactly this idea: it would checksum every file against the copy from the bill of materials in the update and was able to download only the files that were different (by carving them out of the remote zip file using HTTP Range requests).