I know kevlar has a definate shelf life and sometimes vests get rotated out after long use or if they've been stored to long under questionable conditions. Not sure if it's the same with the armor inserts though.??
A few plates have been DRMO'ed and then get sold thereafter, whcih would make them legal to own.
Most of the stuff you see on Ebay is bringback 'oh sh*t, didn't know I still had this, might as well get some bucks for it" stuff. Pretty much anyone who has moved aroudn int eh military can verify you find all sorts of weird crap years later in your closet, garage, and basement.
Plates can get cracks and fractures to them, the only way to know is X-ray checking.
I would walk away from any plates on Ebay. If you are going to spend money to potentially save your life, spend once, spend wisely.
I'd say that its is pretty safe to say that a good percent of these plates or stolen. Call it what you will with cute names like "liberated" but stolen is what they are. I'm also pretty sure that these plates have NOT be DRMO'ed. Uncle Sam is trying to keep his hand pretty tight on these.
Plates are not surplused. They are are not a demill code A (release for public sale) . When turned into DRMO, they are put back in the system. If the US doesnt use them, they are sent abroad as aid. Ever wonder why you see E.Euro Armies in woodland camo and 1990s Ranger Body armor?