What Jeff said...
The separate assortment numbers SHOULD work out, and if you ask Hasbro they do work out... But when put into practice they seem to not work quite as well as theorized. The buyers may favor one over the other for a variety of reasons, the chain may not simultaneously carry both lines, etc... I think if TSC's remnants were sort of forced on the retailers in some way, it would work out...
Around me though, the final TSC waves have gotten the shaft at many stores, and I think it's the routine "ramping up for another line" where they want stock to dwindle before they unleash a new line, a new look, and such.