His itinerary, for example. Or the successful application of covert techniques (as opposed to Manning and Assange).

Less of a factor is that in my opinion, the whole endeavor would be more believably be the result of someone being convinced and assured of assistance, maybe even rewarded, than the courage of a singular man.

Please keep in mind, I value the alternatives where Snowden wasn't recruited beforehand as equally plausible. Not that much more plausible, though.