POW/MIA have been deliberately abandoned before for political reasons.
I have heard reports that over 50 US airmen were shot down over the USSR while on reconaissance flights and were never heard from again. Presumably, some of them survived and were captured. My guess is that the US didn't want the world to know we were doing it (this was in pre Francis Gary Powers days) and the USSR didn't want to admit we were able to penetrate their airspace almost at will. They also didn't want the world to know that we shot down Russian fighters over Soviet soil while escorting these recon missions. I view my sources, however, with the same suspicion I would hold yours. There is so much crap on the net now that you can't trust anything any more.

Whether any of these aircrewmen are still alive is another question. However, I still think my logic concerning Vietnamese-held POWs is still sound.