I keep a file that I call 'individual letters' for just this reason, to keep the odd ones in from incomplete alphas :) Sometimes I just want one letter and it may be in there.
I do this too. I rename them so that the designs for the same letter are together. For example, I put a "B" in the front of the names of all the letter B designs.
Why it's a problem - the person might decide to go back into business and include their previous work on a new site. Or they might die, and a child decides to put the site back up and make some more $ from Mom's (or Dad's) hard work...
I would just save the letters that I am pretty sure I would use-ie. your initials, grandchilderns name,etc. and delete the rest. Make a new folder and title it something like Miscellaneous Letters so you will know how to find them. As AuntAnnie said it is illegal to share designs & I feel like it is akin to stealing from the digitizer.
Sorry, abuch, but sharing of designs is not allowed under copyright law.