One of the reasons I don't particularly like editions is that if you don't print them all in one session, the materials may become unavailable and your vision may change over time, so even if one is going along with the scheme of limiting the number of prints of a certain size from a single negative, it might not make sense to call it an "edition." I'm not selling lots of prints, so perhaps for me it doesn't matter so much, but I'm numbering prints as "print series," meaning the number of prints made from a single negative in one session, exclusive of the possibility of making new and perhaps different prints in another session.