Yes, you will have non-words
When you say you did not need to use the extra words, I guess you are referring to the 9 extras that define themed entries or parts of those. The other 26 extras have terminal letters that spell the sources and author, so you must need those.
I suppose you can fill the grid by guessing the unchecked letters in the thematic entries, but I would think you would need to match the 9 extras with their counterparts to be confident about your grid fill.