I'm having a hard time understanding what you're trying to say.

Salvage rights are very complex on their own, you don't automatically own other stuff simply because you come to their rescue (as in rescuing a ship) or flip a switch. It's quite literally someone else's property. So Starfleet didn't own him.

Second, he's an officer. You have to apply to officer school. Just like the children on the ship aren't automatically enrolled in Starfleet, they and he have to apply. It's a serious application. It's not like this android was just kicking around on a ship and fell into being an officer. (Same goes for enlisted.) *For anyone that doesn't want to read my next longer comment: Data signed a contract to enlist. To sign a contract requires agency, which starfleet accepted.