The other option is to simply go to one of the exchange places like Walmart, Menards, etc.... They charge about $15 to drop off your old empty tank in exchange for a different filled tank. It is easy and you don't have to worry about expiration dates. They don't even look as they in house re-certify the tanks. Typically, they just put a sticker on the new tanks showing it has been inspected and is certified, but no refill station will accept that kind of re-certification.
I have about a dozen tanks lying around from all the grills that I have bought for rehabbing. I offer to sell an empty tank with each grill I rehab for an extra $10. If I have full ones, I sell them for $25. Most of them are expired as far as I know. They use a very cryptic and confusing system for stamping them, and I haven't really got it down yet. And that is if it is even possible to read the stamped letters/numbers.
Returning them to an exchange place is just sometimes simpler although you will pay a little bit more for the convenience.