Unnumbered frame

To give you an example of what I have. I have a 1940 byf - all matching for the exception the frame has no number on it.. Now from my research I can only find that Mauser secretly coded the lugers from 1941 and beyond not prior to that. Now I have a 1940 dated byf??? With no serial on the frame of course which has me confused. This gun is one of two I have, another is a 41 s/42 and come to think of it I have another but can't remember what it is but like the other two no numbers on the frame. Guns are as produced in excellent condition mint like. I can tell you they are not mismatched shooters. One of them is a rig with matching mags, tool and holster serialed to the gun. Any assistence would help me better understand what I have. Thanks