Seized rear calipers

Interesting discovery today on my RRS. Last year I had a very bad vibration from the rear of the truck. I pulled over and was blasted by the heat from the passenger side rear wheel. Turned out the caliper had seized. Replaced the caliper with a rebuilt and left the same pads in that were hardly worn. A couple of days ago I hear a metal on metal sound from the passenger rear brakes. ( sensors disconnected long time ago). I install new pads and then go to the driver's side rear. Lo and behold the pads are not worn a bit on that side. What?, I then realize that that caliper had seized as well but in the off position. Been driving for a year with three wheel brakes.
Moral of the story-- If one caliper has failed better carefully check the opposite side.