They have about 5 tracks and they are played in EVERY episode a few times each. Even the "bad news" sounding music is used in not really "bad" scenarios.
Such as after the leopard scene in the Amazon jungle (Disc 4).
try and remember when this tv show was made. Its not going to have the composition of todays animation and the budget would have been a lot smaller. I think it was amazing for its time. The best animation series ever!
Re-watch just about any cartoon series from the 80s, and you'll notice the exact same thing.
Transformers, GIJoe, and many others reused the same musical cues over and over again. When you're a kid you don't notice it, especially when you're watching one episode a week. When you're older and watching several episodes in a row, it's easy to pick up on.
According to this French page (which contains some selections from the soundtrack!), the series had over 50 musical cues:
It's not just cartoons, it's all shows from all decades. It's as prevalent when I watch Curb Your Enthusiasm with On Demand as it is when I re-watch Air Wolf and the A-Team.