Every series starts with an A suffix, and when the BEP reaches 96000000 it rolls over to the next letter, which would be B, and so on till it reaches the letter Z. Some of the more popular Districts, San Francisco (L), New York (B) and Atlanta (F) typically go further into the alphabet than the others, that sometimes only reach the suffix D or lower. The BEP skips the letters I and O because they look much like the numbers 1 and O.
The BEP does use the letter I as a suffix but does not use the letter O for the reasons stated above. Not trying to be critical or nitpicky, just wanted to clarify.
