Some photographers do editions of prints and then don't print anymore. Joel Witkin is one photographer who makes a limited run of prints of a photograph. There are other photographers who make limited runs and "cancel" the negative. I think in these situations, numbering the print makes sense as it truly is an edition.

I used to print lithographs professionally, and the policy of the shop was that we would never make more than 100 prints of a single piece. The institution running the shop felt that if more than 100 prints were made, it was not a "limited edition." The usual edition size was 50 to 75.

I have to laugh when I see works with xx/500. I saw one print done by a photographer with xx/1000 on it. I asked if he had printed a thousand of them and was told by his sales person, "no, that is the maximum amount he will make of that photograph." I had to walk away covering my mouth so as not to appear rude by laughing out loud at them.