I recently got an older Colt (or so I was told) SP1 upper receiver (no barrel). This receiver has no forward assist and no brass deflector (which you would expect) and large pivot pin hole. The puzzling thing is that it has no markings on it at all. I am used to seeing C H or C M in the rear sight area. Could it be that early SP1 uppers had no markings or am I looking in the wrong place?