your stream of consciousness is correct in a way as I feel the same about filling the sectors, it may have had something to do with a particular drive, controller, or cp/m machine combination. It's gnawing away at me as we type. There has to be something about it out there. So long as the project works, such things can be looked into later.
@foft, @reifsnyderb
8-inch CP/M floppies came formatted with a filler of E5h. Digital Research formatting tools did this. The value also found its way to Atari ST and Amstrad/Schneider formatted FATs as a result. Some utilities simply put E5h as the first entry in the directory when deleting a file. If I recall any of this correctly