My original April 1944 Springfield M1rifle has the milled trigger guard, I think you will find both types during the early to mid months of 1944.
When the Japanesefirst captured M1 rifles during 1942, they re-barreled them to test out in their 7,7mm cartridge. They disliked the en bloc clip and used a stripper clip box
magazine on there M1 rifle copies