GK, it was an accepted fact in the First World War, and I suspect many other, that people shot themselves not to get medals or wound stripes but to get sent home or discharged.
It was often impossible to claim self-harm with the amount of bullets flying around in the front line. It is highly unlikely that they were motivated to seek a medal.
Similarly, as implied, US Servicemen were probably not after a PH or 3 to win medals but to work their ticket home. Any self-harm, to be accepted, would have had to occur where "except when in the heat of battle" could be deemed to apply, ie in the front line only.