Yes, I see there are 67 mentions of OriginalDate in that vbs file. But it's all way over my head.
I really thought other people were getting the original release date from Discogs, whether using Mp3tag or not - and not just MM4 users (the script hasn't yet been made MM5-compatible).
Not sure what I can do next. My searching is not coming up with anything.
Maybe you can get this original release date with the help of it (at least if it is available at MusicBrainz. MB Picard doesn't get data from other sources AFAIK).