Hmm.. done a bit more searching. I cannot find that the letter preceding the serial number corresponds to a year, if there are some system it is more complicated than that since i have found many cameras on auction-sites with the same letter but different year. I feel that i am back where i started, dating the camera to either just before the war or just after assembled from pre-war parts.
A bit of an old post to respond to, but I am going to. The letter in the nuber DOES refer to a year but the 26 letters of the alphabet were recycled so a given letter could refer to several different years 26 years apart. As most models were not produced for more than 26 years, the letter is actually quite precise.