let me tell you, tracking down the exact number of volumes is like solving a mystery itself. The core series consists of 12 main volumes, but there's a whole constellation of spin-offs and side stories that fans argue about including. Some count the 'Midnight Tales' anthology as part of the series, which would bump it up to 15. The publisher's website lists 12, but conventions often display 14 with the bonus content. What makes it tricky is that Volume 7 was split into two parts in some regions due to printing constraints. The series has this cult following where hardcore fans will swear there are 17 'essential' books if you count the artbooks with bonus lore chapters.
Personally, I think the magic number is 12 for the main arc, but I keep all 14 on my shelf because the additional world-building in the extras is too good to ignore. The author's habit of releasing 'hidden volumes' at conventions doesn't help either – last year's limited-edition 'Twilight Interlude' sold out in hours and isn't even listed in most official counts. If you're new to the series, start with the core 12; the rest are delicious icing on an already rich cake.