The Fey Creature template should grant a special ability every 4 HD, or fraction there of.
I took a look at the .lst for Bestiary 3 and I found that it is calculating the number of abilities using the 'HD' tag. Per the documentation: This is the character's HD (Starting HD or Monster HD. Not HD from classes).
It also seems like the BASEHD tag provides the same information: This is the unmodified number of hit dice of the creature in question, as specified with the MONSTERCLASS race tag. If that tag is absent, the variable will return 0.
What is the correct way to calculate the total number of hit dice? For the moment I have HD+TL, but not sure if that is correct.