if I remember correctly, they were slotted & x-drilled intially, but subsequently moved away from the x-drilling in favour of the dimpling or just the slotting I've had mine for ages now and they are still in pretty good shape.
The main problem with drilled aftermarket rotors was that they were often not chamfered properly (or at all). That is the main cause of the cracking. Note that since the parts used in racing cars often had the holes actually present in the casting, instead of being machined in afterwards, they were much more durable. Of course, real racing cars regularly replaced their rotors after an event. Not something that Joe Modder's like us can afford to do...
