Numbers under sight of DWMs

[barr44]

I have three 1917 DWM artillery lugers. After reading one of the previous posts I noticed that there was a reference made to the numbers under the rear sights on the artillery models. All of my artillery lugers have four digit serial numbers.
I checked mine and found out that there are numbers there but they do not exactly match the serial number on the bottom of the barrel. There are four digit numbers under the sight but only the last two numbers match the last two numbers on the bottom of the barrel and these same matching numbers are on the sights. I have also noticed a two digit number on the sight base itself that seems to match the first two digits of the number under the sight.
I suspect that as the barrels were manufactured they were given a specific number. This leads me to believe that the sights were possibly being manufactured in another department and given a specific number, to coincide with numbers on the barrels. I would think that this manufacturing was ongoing in relatively the same time frame. Later a sight was assigned to a barrel and then later the barrel and sight were assigned to a frame assembly and given the serial number of the frame.
This is purely what I can determine from the guns I have been able to exam. Of course I'm not sure what would be the case in the lowered number guns of single or double digit serial numbers.
I would appreciate any thoughts of those who could possibly shed some light on this number sequence.
Thanks to all, barr