Campus Composer // Aqueous Aria

A creature with a prepare spell can't become prepared more than once at the same time. For example, Emeritus of Ideation is on the battlefield and is prepared. When it attacks, its last ability triggers. When that ability resolves, its controller may still exile eight cards from their graveyard, but doing so won't cause Emeritus of Ideation to become prepared a second time or create a second copy of Ancestral Recall in exile.

A preparation card is a creature card in every zone. For example, while it's in your graveyard, Emeritus of Ideation is a blue creature whose mana value is 5. It can't be the target of Zealous Lorecaster's triggered ability ("When this creature enters, return target instant or sorcery card from your graveyard to your hand.").

Only the current controller of a prepared creature can cast the copy of its prepare spell in exile. It doesn't matter who owns that creature or who controlled it when it became prepared.