I guess one of the experts will clarify, but I would guess the thumb-hole was for one-handed opening, thus making the blade illegal for EDC in e.g. Denmark, and the nail-nick therefore was for those markets.
If memory serves, the one with the thumbhole was a promo pic, with a few prototypes floating around. One even escaped the factory and is in the hands of one of our own (sorry, can't recall who has it, but it's a beaut).Unless LM has decided to change the CS in the last couple months, the one with the nail nick is the production model.