The date on the ECU does make more sense, thus why certain '23s can be tuned and certain '22s cannot. More now than ever the date on the ECU is probably correlated to the date the truck is built. But as you said, who really knows exactly?
I've looked at the JB4 several times and just cannot bring myself to do it. It's closer to a 40-50hp increase (rather than double that - at a minimum), and it doesn't tune the transmission. As much as I want to add a tune, I just can't bring myself to spend the same amount of money for a lesser return. If the Livernois tune won't go on my truck, I may just wait until they can tune all '23s.