How do you determine year? - teach a man to fish?

[Texasguy]

I have an interest in a luger for sale and have been researching exactly what it actually is; it's a personal friend selling , so time is not really an issue. Been doing a lot of reading but have hit a roadblock.

I have used the links and info on here to ID the Luger as an "Alphabet Commercial"- 30cal made by DWM - it has a four digit serial number with suffix and all the other markings described on this forum (and other places).

Now, on to the "I am stumped" part - how in the world do you determine the year of manufacture? Is there a serial number reference in one of the books often described on this site? I saw the ebooks for sale - are there references tables there?

I see a lot of "post the markings and pics' responses... I would really like to know where/what the reference material is...versus being told....hence the "teach a man to fish" reference

Thanks