When I was in the Nav
I heard rumors that prior to the U2 shoot-down, over 50 recon planes were shot down over the Soviet Arctic, mostly RB-47s on ELINT missions. Presumably, some of those crews survived, but the Russians wouldn't release the crews unless we admitted they were there.
But again, what would the Russians have to gain? A live American POW on trial is worth a lot more than an anonymous one. And Francis Gary Powers showed we couldn't realistically deny one if he was taken alive.