PDP-11 running RSTS/E had 6.3 filenames, and iirc no sub-directories (each user account (grouped by project) was a single directory). Remembering what “EDS023.DAT” was for could be a headache on large projects.
The edition numbers refer to the manual pages more than the software, which in the early days was under continual development running on approximately one machine. It wasn’t released in 1971.