Have you guys ever noticed this weird little thing about Anime OSTs? Sometimes, Anime OSTs tend to miss out certain music tracks that is played during particular scenes in the Anime itself. The tracks are just normal songs, no vocals or whatsoever, just songs to accompany the mood in the scenes. I observed this since a while back ago. Just to assure you guys, I did the neccesary checking already, and I am 99% positively sure that I did not miss out the tracks in the OSTs, and that I have the correct/complete version of the OSTs. Is there a meaning behind this strange trend? Why do the OST makers want to omit the track from the OST, assuming that it is done on purpose?

Examples of songs that I cannot find inside the OSTs. [The songs play in the background of course. :)]

Clannad After Story
- (http://www.youtube.com/watch?v=0cyNYw5e_X4) *MAJOR SPOILER*
- (http://www.youtube.com/watch?v=qlrK-RjnVv8&feature=related)

K-ON!
- (http://www.youtube.com/watch?v=gKXZKoYtP4A&feature=related) *Ignore Okazaki's intervention at the end. ;)*

Indeed. I've noticed some series doing this for whatever reason, be it using tracks that are not released in OSTs, or including OSTs in tracks not used in the series. My primary assumption is that the anime is incomplete, and it is planned that the unreleased/unused tracks will be applied when another season comes along

Two that I've recently noticed -

Pandora Hearts - Eliot's Version of 'Lacie' in the end of ep 17 and beginning of 18 (can't even find a video of it); the closest I could find in the OST is this version (http://www.youtube.com/watch?v=DhmRKlIOVg4), a solo piano arrangement in a different style played with more rubato. For some reason, everyone else seems to be oblivious of the fact that the acclaimed piece was never released...

ef - a tale of memories - the piece used in the trailer (http://www.youtube.com/watch?v=WUwr2tA8res), which was actually a pure instrumental mix of two themes that were later used as part of opening songs as well as major themes in the OST. Fortunately, while this was never released, one can at least get a decent quality audio rip from the trailer.

Anyone else have any insight?

I do know that occasionally you'll find a CD on a series entitled "Out Tracks" which are basically the tracks that were left out of the main OST, but vary rarely are they actually known of (in fact, the only one I own is of the Fate/Stay Night anime).

The real situation is that OSTs are established with two constrants:
They must be released within the first 6 episodes of airing, otherwise sales will not be very good. This is because general fans will quickly lose interest in owning a OST after this time period.
The limitations of what can fit on a CD. There's only so much you can fit on a 80 minute disk. Having every variation of a song is not the best way to use up disk space. Instead, they put the most prominent tracks on the main OST and then put the rest on what I mentioned before: out tracks.

There's one missing in Final Fantasy VIII [8] playstation game
I'll let the nerds find that one out themselves if they give a monkeys' about it