Bought books that are now part of a collection, and I would like to buy the collection but not pay for previously boughten books. Is this possible or will I have to pay for them again? (Tsd training mechanics collection)

ipad mini 2 retina

ios 8.2

i bought some books about automotive engines by TSD training. A total of 3 books.

Earlier i was browsing the iBooks App Store and noticed these books were now part of a 14 course mechanics collection of books.

I wanted to buy the remaining 11 courses (iBooks) in this collection thinking I could just "complete my album" per say as you can when purchasing a collection of music on a given album but it seems I do not have this option. Will I have to pay for these 3 books again if I buy the collection? is there a way around this? Can I choose only the remaining books I need? Any help is appreciated. Thanks in advance