Yes, every country has it's own system for aircraft designation markings. While American civil aircraft have "N" numbers like the one mentioned in the article, many countries like Canada and Great Britian use nothing but letters, such as CB-FXT.

There are also various military numbering systems but I don't recall ever seeing a US military aircraft with an N designation. That further makes me think those men were CIA (aside from their flashy clothing that just doesn't fit in the snake-eater world). Good idea looking up the N number in the civilian registry. It doesn't surprise me that the number could be phoney. Yes, a Pitts S-1C is a small single seat aerobatic biplane, hardly a transport of any kind.

I know a man who used to fly for Chenault's airline Civil Air Transport (CAT) in China following WWII. He left China shortly before the communists took over. CAT was later purchased by the CIA and renamed "Air America." Supposedly, there is another outfit called Southern Air Transport that does the same kind of thing.