I don't think POWs were very well situated to make this judgment.
Wrong. POW’s are always in a position to get an inkling on what is going on. Many times POW’s have been able to create relationships with one or two or several guards and information is gained. In addition, guard attitudes change, rations change, POW’s see more discussions between guards, tempers may flair, and they can hear the bombs falling.
PLEASE don’t think that when a US Soldier gets captured he considers his duty finished until his release. There are always de-briefings on information a POW’s may have gleaned after their release. POW’s continue their obligation to the best of their ability even during imprisonment by the enemy.