A very true observation, regarding the NST. They're less common than the normal "N" or "S" dials, but are certainly more plentiful than any of the others. I think these, just as Daytonas (which aren't rare by numbers), become "rare" by condition relative to the other known examples. The 2447NST in the Heuer Parade sold for $30K without bracelet, and while I don't believe the handset to be correct on the 2447NST in the GWA8 auction, I think the dial quality was superior and the cases were of similar sharpness. Up to the market to determine if a handset reduces the value by 50%, but I feel that more was at work with this auction. I feel pretty confident that if you have a chance to buy a rare 60's Carrera variant at a reasonable price at this moment in the market, you won't regret the decision.
GWA 8 Example: https://www.phillips.com/detail/HEUER/CH080218/68
Heuer Parade Example: https://www.phillips.com/detail/HEUER/CH080317/9