The OS and Main is what's used to tell this as far as I know and they match the version 2.0 in mame. The 2.0 and 2.3 probably come from rom labels of the program roms. Anyway you should be able to upgrade your board to 2.3 if you replace the program roms. You could probably dump them anyway if you have a programmer to check if they flubbed an update by not updating the OS and Main code but I wouldn't mail anything out based on this.