My apologies if this has already been suggested (another suggestion I have is adding a Search feature to the forum).
When I am looking for matches, I check ISBNs. However, I know from my work as a librarian that different ISBNs do not necessarily mean different content. I am really glad you have the linking ISBNs feature in place, but I wonder if you could enable us to suggest other ISBNs to link.
I gather that you are trying to balance between bibliographic distinctions and similarity of content. For me, as a cook and librarian, the worth of EYB is in the indexing of the content, not as a narrowly focussed LibraryThing. So when I come across a situation where my edition or pritning isn't in your database, I have been choosing the closest match. However, if one version of the title has been indexed, I'll add that one to my booksehlp, even if it doesn't match so well. It's much more important to me to have the indexing than the bibliographic detail exact.
The example in front of me is Edna Lewis' The Taste of Country Cooking, which has a few linked ISBNs already, but not the ISBN on the item I have, which is for a Knopf hardback published in 2000.
Thanks for considering this!