I discussed ROMs with Scott by email back in 2015. Scott very kindly compiled all of the ROM files that he still had at that time and sent them to me. With regard to Frantic the only version that he still had matches the one he posted here in the first post. To quote Scott, "this is the last version of it that I have".
So unless Joe, or any beta tester, has a later version then it may well be lost to time.
Now that being said, over at AdamArchive.org there are two versions of the ROM to be found. The one labelled [a1] is different to the one here so perhaps that is a later version?