By the time of Muhammad according to my understanding the Christians would have referred to their collection of books as "the Gospel" and the same for Jews with the Torah, so its not that surprising.
Again. This is about what the Quran is saying.
1. Nevertheless, you think the Christians referred to their scripture as "The Gospel"? Not "the Bible"?
2. Dont you think that "People of the book" sounds like its one book? Al Kithab. The Book.
3. So should not it be "People of books"? or something? So should it be Kuthub instead of Kithab?
4. The Quran refers itsself as "The book" or "Al Kithab" right at the beginning. Zalikal Kithaba la raiba feehi. So does that mean "People of the book" must be referring to the Quran itself? Afterall, its the same word. Al Kithab. The Book.
5. Thus, thinking of all of this, people of the book who are Jews and Christians with their own written down books in book form, when the Quran says "we have sent down to you the book as a clarification" in lets say a verse like 16:89 which book is it referring to? People of the book must be with "the book" so which book is the Quran referring to in the verse 16:89 which is supposed to be a clarification for all things etc etc?
I am only following your line of reasoning. The book means a book that was written down. That was your reasoning. So what do you think of these points?