So I spent the last several days painstakingly adding every paper rare and valuable common/uncommon I own to a deckbox collection with the sole purpose of then exporting that collection into mtggoldfish.com (since mtggoldfish doesn't appear to have a mass card entry option).

My reason for doing this is to take advantage of the mtggoldfish SuperBrew feature to help me figure out what decks make the most financial sense for me to work towards in different formats.

Unfortunately, I didn't realize that when I was adding cards to deckbox via mass entry, it was not assigning a set to the cards. Now when I try to export my deckbox collection into mtggoldfish, almost every single card needs to have a set assigned to it before I can upload. I have thousands of cards in that collection, and I am hoping some smart person here can suggest a better solution than spending hours assigning sets to each card in my deckbox collection so that I can upload it to mtggoldfish.

Yeah, I saw your post about this on Reddit. Unfortunately, I really doubt there is a way to do what you're describing - not specifying the set leads to genuine ambiguities that only your manual input will be able to resolve.