Look at a bunch of IDs in posts here. Can you find a single ID where ANY of the six characters are any of these letters:
ghijklmnopqrstuvwxyz
Come back when you have one, and reference the post to show us. We'll be amazed and transfixed when you do it!
Until then, the rest of us will continue to believe that all IDs are built from the following list of 16 symbols:
0123456789abcdef
(sorry if I'm responding to a shill. I may be. But I know some people don't know what hexadecimal is, and might go "it's a letter!" when seeing "c" and not realize that a-f are special in this context. So trying to be clear.)