What do you mean by 'static' ?
Probably that it not easy to replace this sound-script.
Here is an example of what happens with sound script 0x31 :
This sound script is made of several fragments (let's say A,B,C,D,E,F). Each of these fragments can be stored anywhere in the roms (they are not always contiguous).
Sound script 0x31 is designed so that the sound is played as ABBBBBBBBCDEF. This can save a lot of space because B is played several times but is only stored once.
If you import a sound like GHIJKLMNOPQRS over this sound-script, fragments H,I,...,O will be stored at the same place (previously B)... and the last one (O) will override all the other ones. Thus, the sound will play as GOOOOOOOOCDEF.
At the very begining of sounds script 0x31, the same guitar chord is repeated several times. To save space into the rom, Stern has used the same sound fragment for each note.
Quoted from markmon:
I wonder if perhaps pinbal browser just doesn't enumerate all the tracks and such thoroughly on white star
I have checked on T3 and LOTR (but not on Elvis) that the sound roms are completely referenced in at least one sound fragment. That means that there is no sound in the rom that is not listed in a sound script.
However, some sound-scripts might be 'code-orphans' (never played in the game) but I have no way to list them. We've already seen this in Sam games.