Model 1917 bolt sleeve Notched vs un notched serial # of change?

I noted in all the publications, they note that later Model 1917 bolt sleeves had a notch added.
sometimes called a "take down" notch, to aid in bolt dis-assembly.

But no one seems to know when this change may have occurred?
Is this still an unknown serial range or date?

Thanks to those who know, or may be trying to find out.