The whole issue of linked books is one we are planning to tackle when we have the mammoth task of our new search out the way (mid-August, hopefully). We took the view that a lot of members would want to have the edition they own on their bookshelf, with their own cover displaying. So that meant we had to list every edition separately. However, once we index the book we need to link it so the recipes appear for every edition. Once a book is linked it doesn't appear as a separate listing though can be accessed by clicking more detail for the indexed master, which displays all linked ISBNs. With the new search the linked books will display by ISBN, format, country and date of publication which should be enough to identify the edition you own.
Part of that review is sorting out how all comments, ratings and Bookshelves can be amalgamated for all editions of a book.
There is also the issue of books with no ISBN number that we will also be tackling as we know a lot of members have older books they would love to add to their Bookshelf. In the meantime, for your MFK Fisher book I would look at all the EYB book details pages for the books which will list format, publisher, country and date of publication and see if you can match your edition. Amazon and abe books may also list more editions with covers so you may be able to do a match that way. Sorry this is rather laborious but without an ISBN it is much harder to identify editions.