When Geiger was writing his offsets guide he seems to have mistakenly assumed that the BRR samples start with "(00) Silence". They actually start with "(01) Clap". As a result the labels for the samples in the offsets guide are all off by one. The last valid instrument is actually 3E, which seems to be a
cuica.
I put "unused" in quotes because it actually does show up in the instrument table for the "song" "{4C} Lavos Breath", but that song is all crazy noise effects that I don't have a full understanding of. It never actually plays it as a straight instrument sample.
