Barry:
The one in your link says 6 conductors at one point, and 4 conductors at another point. Apparently the seller is clueless.
By the way, there is no "RJ12" cord. In fact there is no RJ-anything cord. Cords are named by the size of the plug, and the number of conductors present. There are straight-through and crossover types in most sizes and conductor counts.