Rule 435.1.b

When one or more cards become Detached, they cease to be in the Attached state.

• 435.1.b.1 To represent this, these cards should no longer be placed under the card they were previously placed under as Top-Most…
• 435.1.b.2 If the Top-Most Card no longer has any cards Attached to it after this, it is no longer a Top-Most Card.

Official Core Rules