An ability that triggers "whenever you fully unlock a Room" triggers when a door becomes unlocked and the other door of that Room is already unlocked, or when both doors of that Room become unlocked simultaneously.
Restricted Office // Lecture Hall
Each Room card is a single card. For example, if you discard a Room card, you've discarded one card, not two. If an effect counts the number of enchantment cards in your graveyard, Bottomless Pool // Locker Room counts once, not twice.
Some abilities allow you to unlock a door of a Room you control. You can't choose to unlock a door that's already unlocked with such an ability. If such an ability requires a target, you can target a Room even if both of its doors are unlocked, but the ability won't do anything when it resolves.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Scott Buoncristiano
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