I should also add that one private school I know of relies heavily on adjuncts and there were a FEW who went over the two courses/semester on a pretty regular basis. That's no longer the case though as the programs decided to spread the adjunct-taught courses over a wide pool of adjuncts to avoid (a) single-point failure problems of an adjunct suddenly leaving, and (b) potential future legal claims by an adjunct of actually being a full time employee and seeking back pay and benefits.

I don't know how serious the (b) aspect was, but in the corporate world I know it was a constant fear and we had all sorts of regs to follow about that.