If you hold the legal entitlement to particular sats, you own them. The entitlement is composed of 4 elements: 1) in kind enjoyment, 2) monetary compensation, 3) transaction initiation choice, and 4) transaction veto choice. If someone is holding their keys, they are meeting the structure of a property rule entitlement. Moreover, it isn’t merely a number, it’s a particular number in a particular context.