Another thing to note. The Final ROM Archive has good approximations of build dates for most of the final builds of games. This is very very important to SEGA history, because we essentially have a reference of when certain games could have been available in the market. Since a lot of the release date information on the earlier games are completely missing or ambiguous, the archive might be able to help pin point when the actual retail release might've taken place. There are some games that have obviously wrong file dates, but most of the ROMs that did match with the finals seem to be okay.
There are some games that were kinda hard to identify either or not they're actual prototypes or just revision prototypes (something meant for after the initial release ROM).
is a strange one. There are no apparent differences from playing the game a little bit side by side with dual gens, but comparing the bytes between this and the US final is a different story. I used saxman's tools to take a look at the ROM to see if I could find maybe some alterations in layout or graphic data but nothing really jumped out at me. The weird thing though, which might have been a side affect of using saxman's programs on a ROM with different pointer locations, is that this build contains four extra maps that appear to be duplicates of some other level. This might imply that this is an actual late prototype of some kind, but again I'm not entirely sure. Hopefully saxman takes a crack at this ROM since he'll know more about it than either drx or I. :P
Another weird one was Golden Axe. It's definitely a prototype for REV01, since the ROM header hasn't been renamed to reflect the new revision number (you'd be surprised how frequently developers simply forget to update the month/year/product id information until the last minute). But the strange thing is that upon loading into the main game, the game will literally pause itself before your character appears. I have no idea why this happens. I thought it was some debugging thing, but it seems rather pointless (unless of course you could pause the game at that point to look at the RAM contents or something...). It's not like level select is enabled by default or anything. Might be worth checking out.
Another weird curiosity are the files that are denoted Japanese by the "JP" tag at the end of the filename before the extension. Almost every single one of these are legitimate prototypes. Another thing to note, that almost every third party non Sega developed/QA tested game before 1993 is a prototype or revision prototype of some kind. DRX and I thought this was because the earlier contents of the archive were mistaken with ROM submissions for Sega standards, since many of the different ROMs present have basically the same things going for them. Pretty much every different ROM we found that had noticeable differences upon playing the game would lack copyright information or other things that would go against the things SEGA themselves required from every game at the time.