Good question. I decided on letters early on and then I assume the reason I wanted letters stopped being true at some point. e.g. I think I wanted to make the first letter relevant to the entry at some point?
Do the letters cause you an issue?
I understood. The concept was changed in the process :) BTW, the initial idea may be was interesting.
I haven't played yet, but it seems to me that it would be more convenient and familiar with numbers. At least with numbers, it's easier to search than attempt to remember the alphabet.
But this game seem be interesting in any case.