Many titles that I want to acquire are available in hardback and one or more paperback versions - each with a different ISBN number.  I don't care what version I get.  If I add just one of the versions to my Wish List, will the system alert me to the availability of any of the versions of that title, or just the specific ISBN number I've added to my list?

You will get an email that a similiar book is available, it seems to go by title / author.

It only works if the different book listings (paperback, hardback, etc) are connected in the PBS database, though ... not all of them are.

You can make sure you get notifications by checking it off in your Settings. It is a global setting, meaning there may be times you listed a particular book and only want the hardcover version, but you will be sent a notification every time a paperback of that gets posted. It can become quite annoying. If you have the room on your WL, it might be better to add to your WL the separate formats you are interested in.

I second EveDallas's idea. Sometimes many versions/isbns have their own wish list lines.

Good luck!

The similar book notification very rarely works for me, I know similar books are being posted but I don't usually get notified.  So if you have room on your WL, I would suggest putting every version on that you are willing to take.

"Sometimes many versions/isbns have their own wish list lines."  

Yes, you could be #8 on one wish list and #12 on another, but you don't know which version will come in more often. You will NOT be notified by email of another version being available until there is no WL for that book at all. You might as well put yourself on both/all WL if you have the room. You are allowed 200 books on your WL.

The email is only for books that aren't WL. If they are all WL then you need to put each one you want on your WL.  Yes it uses up WL space but it's the only way.  It will only send an email if a different version that's not WL is posted.