I strongly suspect the order of filenames and the order of files in the archive line up, this at least appears to be the case in No Mans Sky (pre-HGPAK) and Ratchet & Clank, but I need a bigger sample size than 2. If true we can omit the whole hashing step.
Has anyone encountered PSARCs that have unordered filenames? Would it be possible to create a special build that verifies if the filenames are in the same order and then tells people to leave a reply here with the result?
I'll be testing various PSARCs later next month.