How is it that the college bookstores can sell you a textbook edition that the publisher says doesn't exist?

I know that the bookstores package bundles and change the ISBN numbers and all. But I'm smarter than that and search for the right edition to the required books and just buy them from students that used it last semester. However this term I have Music 100. They require The World of Music by David Willoughby with Connect Music (this is the online access where the you can take test and all that) edition 9. I couldn't find that edition anywhere online used or new so I called the publisher McGrawHIll and they even said that edition 7 is the latest version they don't have an 8 or 9. So I go to the teacher and ask him what version would be acceptable as the publisher has no version 9 out there. He sends me back an email stating that this term they are switching to using edition 9 with the Connect online. WTH!!! I could understand if they bundled and changed the ISBN and came up with some astronomical fee to charge but they are scamming me for believing that there is an edition that the publishers are unaware of. Hmmmm how is this possible? Anyone have experiences like this?|||Since something is obviously wrong I would just go to the bookstore and ask to see the assigned book. I'm familiar with Connect when used with the Kamien book (Music: An Appreciation) but the most recent edition of that book is the 10th. The 7th edition of your book is brand new, 2012 copyright and you are extremely unlikely to find it used anywhere since it was published toward the end of the fall semester.|||You may have the wrong edition or got someone in the publishers office who did not know what she was doing./