Serial number suffix questions

Hi everyone,

Here is another "newbie" question for everyone. I figure this may help all of us newbies. I was wondering about the letter used as a suffix for the serial numbers on Lugers. It is my understanding that the manufacturers used the letter suffix so that the serial number could be used again as production continued. Also that not all letters of the alphabet were used for every model of Luger produced. Now my question is whether or not any letters that were used are less common than others and what letters would you say are the least common. Also, does this affect the collectablity of a Luger? Does it matter whether the Luger was given an "a" as compared to a "z" in relation to its collectablity? Another question, Were the letters ever combined or just used one at a time? Thanks in advance to any and all responses to these questions.

Sid.