I'm not sure how we could show you what was on your Bookshelf before you added the ckbk catalog. I'll have to give that some thought (suggestions welcome too!).
All I can suggest is that you remove the ckbk books from your Bookshelf, from the same place in Bookmarks that you added them. Note the number of books on your Bookshelf. You can also download this to a spreadsheet, explained here in Help. Now add the 743 ckbk books to your Bookshelf, again from Bookmarks. Take the new books number on your Bookshelf, deduct 743 and deduct your old Bookshelf number and the negative number you now have is the number of ckbk books you already owned. However that just gives you a number, not what they are. Depending on how familiar you are with spreadsheets, you can identify those books by finding duplicates between your old and new Bookshelves. Download your new Bookshelf data. Copy your old Bookshelf into the new spreadsheet and then use Microsoft filters to find duplicate entries. This is the MS Help Page that explains how to do that.