The units recognize the software versions by what's currently on the unit and the x.bin update file name. As long as you have room left on the card, you can keep multiple update files on it. Since HB only keeps the latest version software on their website, it is recommended to keep a backup copy of the update file. So, I generally download from website to my computer and only put one update file at a time on the SD card to avoid any potential issues. I keep a separate backup file on the computer and a spare thumb drive. Note: If you put multiple update files on the SD card, the unit will only recognize a same or later version so if you need to revert back to a prior update, you would have to remove the later versions from the SD card.