As I try to get a handle on the incredibly numerous variations within "basic" and "original" D&D, I've come across a few sets of books that are related by some common title that doesn't seem well documented. I found six books whose covers are emblazoned with an indigo banner that says "Challenger Series." It doesn't seem to be related to any actual level of play, since one of the books (the Creature Catalog) is "suitable for all levels" and another of the "books" is a DM's screen.
Yet another book, "The Night Howlers" is both "Challenger Series" and a "Creature Crucible."
What, if anything, does "Challenger Series" signify? (And is there anything more to "Creature Crucible" than "it's a book of monsters"?)