The designation "Alphabet Commercial" was coined, I believe, by Jan Still as a more accurate designation of the post-WW1 commercial Lugers with a suffix letter in the serial number. Why more accurate? Because they didn't begin production until mid-1921 and thus 1920 is inaccurate.
The reasons they are less popular as a collectable are 1., they were produced in greater numbers than any other variant are are thus the most commonly encountered and 2., the vast majority are in 7.65x21mm (.30 Luger) which isn't as easy or as cheap to find as 9mm. You may also add that as a commercial gun they have little to offer historically.
A few do have collector interest. Among those are the few made in 9mm, those that can be identified as police issue and the M23 Finnish contract military Lugers. Germany was in great need of hard cash so I believe that most of the Alphabet Commercial production was exported.
WRT the "frosted" bore, cleaning it with JB Bore Bright IAW the instructions should reduce the tendency to copper foul. Bore Bright is a polishing compound and will remove all current fouling in the bore and also polish it.
I've owned - still do - a number of Alphabet Commercial Lugers in 30 caliber and without exception they have been reliable and accurate. Below is a reduced size 50 foot target shot at 54 feet with an Alphabet Commercial Luger.
