I am not sure but I think I have seen them at wallmarts for 3-4 years. The manuel says 10/01 on a date somewhere but I have no idea if that applies to the detectors.
Concerning the item below (from my original message, a gal at Bounty Hunter said that they don't show the 505 because it's sold at Wal*Mart. (I forgot to ask her how long Was*Mart had sold them.)
The Bounty Hunter home site (detecting.com) has absolutely nothing about it.