Wondering why NiGHTS Bonus Stages songs aren't part of the official OST

[Pico]

When I was listening to the game's OST, I noticed that the themes for the four NiGHTS Bonus Stages (which I'll not spoil here for those who don't like spoilers) aren't within the soundtrack. Is there a reason why this has happened?

(Don't worry. I won't be mad, no matter what the answer is.)

 

[Dima064]

If I'm not mistaken, these are taken straight from the original NIGHTS game. That's why.

 

[Pico]

I understand. Thanks for the information.