I think I should clarify, I wasn't clear. I think when the editions are in markedly different sizes, and the photographer is completely upfront, it is a reasonable practice. For one thing it might allow someone struggles financially who wants a particular print to afford it in a smaller size. I am referring to persons who change the size a tiny bit. I have seen this. While a practice like that might follow the letter, I feel it is deceptive.
A while ago I read an article by Brooks Jenson. It was called "What Size is the Edition?" In typical Brooks fashion he makes a cogent argument against editions, agree with him or not. I found I agreed in principle with his reasonings, and decided to stop editioning my prints. What I found was that even though I felt Brooks reasonings were sound, that open editions did not sell nearly as well. What I wound up doing was going back to editions, but I set the limit at ten. Now that seems low, but the truth is for me, ten is plenty, and creates a true (although artificial) rarity. I'd rather have 10 of 10 out their than 2 of 500. Clearly this is what works for me. If my prints get to the point where ten isn't enough, I might raise it to twenty, but presently it takes me a at least a year or more to sell through ten. The nice thing about this is when I get the print dialed in it doesn't take me long to run off ten + one for myself or my mom. That way when someone wants one I can just pull it out and mount it. I don't have to fire up the darkroom and print it.
I hope I haven't gone too far off topic, but I think anyone interested in the whats, wherefores, and whys of editions should read the article:
Dead Link Removed
As I said, a cogent and well thought out position that I mostly agree with in principle, but do not practice, as a practical matter of economics. In other words sales. I need to make a certain pittance to keep printing.