From which sources do institutional participants in Bitcoin ETFs acquire their Bitcoin? Why do these transactions not have an immediate impact on the market price?
Is this lack of price reflection due to the fact that purchases are made in OTC through exchanges like Coinbase, which sell, let's say, "papers" assets and not the actual Bitcoin? 

 That’s a lot of big swollen bags. 

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 Is there any proof-of-holdings if such a thing even exists for all ETFs?
I mean, there could easily be a difference in stated holdings (bitcoins on paper) IOUs and the actual bitcoin in reserve (if any), no?