[JulianMorrison]

Determining whether a thing's a single stream would be down to finding where it touched down in the world of either fiat currency exchange, or purchasable stuff.

I don't know if it's NP complete. But my guess is no. I can immediately think of algorithms (maybe crude ones, I am no statistician) that could be used to attack it, and they require a lot of iteration, not an explosion of recursion.