Lt. Col. Julian Hatcher is indeed on record as recommending addition of a left-side gas vent hole in the M1903 receiver. In response to Lt. Col. Hatcher's recommendation, Springfield Armory replied that they had already been experimenting with the hole. So, it's problemmatical whether Hatcher originally instigated the hole. Nevertheless, the hole got added and Hatcher's recommendation certainly helped it along.
For the record.
J.B.