Question about Book Editions

I'm curious how the recommendations feature takes into consideration the different editions of a title. If you own one edition will the same recommendations be generated from that title as would from a different edition? Same question for the similarity to other members feature. I ask because I toggle between wondering what the usefulness of having multiple editions of books in the database and knowing that this is part of classifying your collection and knowing who has rare editions or fairly common ones, etc. Also, many of the editions I own for classic books are old hardcovers I've picked up at yard sales and so on that don't have jackets and are before ISBNs were included on the copyright page. I've been choosing to add the version from the search results that is clearly not a recent edition. Just wondered what other people thought about this.