By the way, I have seen the problem with the 680 manual saying that is only starts after a certain serial number. This is actually listed this way on their website, too.
With SubZero, you should always plug your part number into the distributor website and check for serial breaks. Often times there are several serial breaks that will point you to different part numbers for your particular unit. This solves the issue with the 680 manual. Look up your part, plug it in to the website, check the serial breaks and it should list your particular range. They can make minor changes several times throughout the different iterations of the same model number. Twicksters can be twicky that way.