Both of my KE-Grades, a 12- and a 16-gauge, have a four digit number on the parts just like yours. I've heard it refered to as an "assembly number" but I don't think anyone really knows.
I don't think anyone has really decoded those letters and hashmarks down the barrel tube bottoms. I've posted this information before, but if someone with a lot of Remingtons, like Bobby, add these to what he has and what is in Charles' book, maybe a pattern will emerge.
1906 12-gauge KE-Grade has /// K E Y
1909 16-gauge KE-Grade has X K E A1
1896 12-gauge AE-Grade has P A
1906 12-gauge FE Trap has /// F E G 13
1894 12-gauge BE-Grade has B J and a poorly struck E or an F
1907 CEO-Grade 12-gauge has /// M
1905 DEO-Grade 16-gauge has X O
It is beginning to look like an X on the tube bottoms might have something to do with 16-gauge?!?
