results from Google seem to confirm that, although possibly for different reasons...
Originally Posted by google?
It's not really the surface slots that matter as for direction.
On some high performance rotors, the interior veins are curved to improve air flow. That is where rotation direction matters.
Most basic rotors have straight veins and it matters not which side you put them on.
If they are marked L & R, they prob have curved.
These arent marked, and I dont think the vanes are curved, but I have not really looked. Will report back.