a real world point of view
The following list of novels per Doctor highlights the number of stories have been told with each incarnation in the form of an original, non-anthological work of prose. It therefore does not include Short Trips, 2-in-1 books, direct-to-audio books, or Target novelisations — but it does include Telos novellas and Quick Reads.
Though care has been taken to get the right numbers, its methodology is obscured by the fact of its simplicity. No attempt is made here to tell you which books are included. This page merely presents information mathematically, so that the lists can be easily sorted and you can walk away with generally the right idea about a particular Doctor's "footprint" in novels.
If you think something is wrong on this list, and your correction is more than just adding on the latest novel, please present your sums at Talk:List of novels per Doctor.