Not, it was not batches, its was luck of the draw. Heat treat cannot be done by eye in varryi8ng conditions, plain and simple.
ALL early 1903s were subject to brittle receivers.
That said, most that survived had been fired and no issues (Marines on Guadalcanal >
I would take it in a heartbeat. I am not concerned.
Someone else that is, good enough.
The 1917 did not Supplement the 1903
The 1903 Supplemented the 1917, 75% of the WWI rifles were 1917s.
Just because a Receiver cracks with a hammer blow, does not mean it can't take the pressure.
If it does go, then is a lot of shrapnel as opposed to a 1917 bulge.
What people ignore is the unsupported head of ALL 1903s, and that is far more likely to blow trough and get you than the receiver as the gas path is not controlled.
And I saw a modern Model 70 blow up recently and it was pretty well shattered.