Grip Numbering on Late WW-I Lugers

[Luke]

Have recently seen two late WW-I Lugers, a 1917 Navy and a standard 1918 4" military, with good grips which are obviously authentic but NOT numbered.

Both sets have an upper-case letter on the inside of the left grip and nothing else.

Does anyone know if DWM discontinued numbering grips near the end of the war, or if they were just inconsistent at that time?

Or, does the upper-case letter inside the left grip indicate that these are armorer's replacements?

Would appreciate any information and/or similar observations by other collectors on the subject.

Thanks,
Luke