1997 seems like it must have been quite a year in the philosophy of mathematics. Mike Resnik published Mathematics as a Science of Patterns, and Stewart Shapiro did Philosophy of Mathematics: Structure and Ontology, which are two strong arguments in favor of different versions (I think) of structuralism, which had been a popular idea over the previous few decades, but I think not terribly well-developed before those books. At the same time, John Burgess and Gideon Rosen outlined and attacked fictionalism in their A Subject with no Object, and Penelope Maddy advocated an end to all this investigation into the ontology and epistemology of mathematics in Naturalism in Mathematics. In addition, Synthese did a special issue on proof in mathematics, and in 1998 a couple other important books came out – Mark Balaguer’s Platonism and Anti-Platonism in Mathematics and the collection Truth in Mathematics edited by Dales and Oliveri.
I don’t know of any other particular year that had such a proliferation of interesting books coming out nearly simultaneously in one relatively small area of philosophy like this. And I feel like there’s another book from 1997 that I’m leaving out as well. Does anyone know any other examples of years like this?