In light of the recent history, 0% seems unlikely. Holding to the question - “Does "purchased" #Bitcoin left on an exchange really move the price?” - I’m just thinking that unless there is 100% paper bitcoin at these places, the answer has to be yes, the price would “move”. Seems more likely that they only put some of it in, so new purchases are likely to move the price proportionally to the fraction of paper bitcoin the exchange is carrying.