The original cones do not have one less rib. None of the varients that i am aware of (and are listed in the service docs) show any other configuration. there was a ribless cone made for the L (that wasn't a B cone) but that wasn't for the series 2 or pro-line. It was the original SRO that became the very first EVM-15L, but those are very rare (I've never seen one). Also, a tapered cone (conic section) is not correct either, the L uses a curvalinear cone which is an exponentially curved surface.
The speaker repair world, just like the tube world, is full of misrepresentation, cheats and counterfeits. The "one less rib", and "taper" screams misrepresentation, though if it sounds good to you it's fine for your needs. With my customers, if it's an aftermarket part (sometimes necessary if the original part is no longer available), it's represented as such and is thoroughly tested to be sure it's reasonably close to the performance of the original.
There are some drivers that do not have suitable aftermarket parts available and the original part doesn't exist. For these, it's a total crapshoot and I usually avoid this unless the customer is on board to take the risk.