That is typical NS customer service.
Quick response time? Check
Detailed and clear answer? Not so much...
The stuff about the Proto is all correct, but the bit on the SL requires clarification/correction: The SL is directional because the inserts have setback and also because the sidecut has setback. So just centering the bindings does not make it a true twin.
Didn't they say that the side cut was symmetrical?