Before you accept an exchange 20# propane bottle

Confirming another post here:
I have a propane dispensing station, and assure you propane cylinders must be re-certified 12 years from date of manufacture, then again 5 years from that date.
In my area the standard customers' joke is, if they present an out-of-date cylinder "that's OK, I'll take it to Wal Mart and exchange it for one in-date"