Some spells have "while prepped" effects that specify they can only be used once per turn. This should be interpreted as once per turn, per instance of that prepped spell. This means that if you have three copies of the spell prepped, you can use the "while prepped" effect three times. If a spell is returned to your hand, allowing you to prep it again, the while prepped effect could potentially be used twice for that copy of the card (once while it is initially prepped, a second time after it has returned to your hand and been prepped again).
