Thanks Striker!
To clarify, military Lugers were numbered in blocks of 10,000, with a small script letter designating the block. 5 digit serials were generally commercial reworks.
It would go 1a-9999a, then 1b-9999b, etc etc.
Since production rarely exceeded 260,000 guns per year, the alphabetic serial number plus the year or year code of your gun should pretty well pin it down.
Now, in the past, folks have made the same mistake of NOT including the little letter, and that's where it got hairy, especially if any of them were reported stolen.
Many guns of the same year *could* very well have the same serial this way, as without the alphabetic indicator, up to 26 guns out of every 260,000 would be numbered and marked identically.
This is why very few Luger collectors will ever post their full serial number in correspondence or in public.
NOT because it is a hot gun, but because it could be erroneously on a hot list after one of it's number twins was stolen.
Edited to add:
PS, It doesn't seem to help matters any that the little letters are written in *German* handwriting type script, and are very easy to confuse in and of themselves.