I actually ran into the same thing last week when I went to the U-Haul place to get my BBQ tank refilled. The tank was stamped 10/77, a little more than 12 years old. However, a few years ago when the valve change came about, my other fill place just exchanged me this tank for my old one but there wasn't a re-certification date on it.
When this tank is empty, I'll probably do the Amerigas deal or dispose of it. I'm like the guy in the previous post, I have two on the trailer, one and a spare for my BBQ grill and one for my wok.