I would like to know what are the most sophisticated ways to estimate the amount of bitcoin that has been bought globally with various fiat currencies. Exchange data is only one source, and may well cover a large percentage of value that has been transferred but I can't help thinking there must be a lot of "off exchange" trades going on which may well account for a lot of value. I would also consider fiat money spent on mining investments including implied energy costs as a transfer of value.
I'm wondering what is the opinion of the community on the best way to measure how quickly fiat value is being transferred into bitcoin?
To put it another way, what is the shared "stake" in bitcoin?