I believe the licensing agreement dictates not only a specific maximum number of copies, but also a time limit, whichever comes first. Hence, certain sets will go out of print having sold fewer than the maximum allowed.
I can't confirm it, but it makes sense, as the rest of the band is Fred Katz, Paul Horn, John Pisano (listed as "Asano"), & Jimmy Bond. And, of course, Chico's given name is Foreststorn Hamilton.