603.6d Normally, objects that exist immediately after an event are checked to see if the event
matched any trigger conditions. Continuous effects that exist at that time are used to determine
what the trigger conditions are and what the objects involved in the event look like. However,
some triggered abilities must be treated specially. Leaves-the-battlefield abilities, abilities that
trigger when a permanent phases out, abilities that trigger when an object that all players can see
is put into a hand or library, abilities that trigger specifically when an object becomes
unattached, abilities that trigger when a player loses control of an object, and abilities that
trigger when a player planeswalks away from a plane will trigger based on their existence, and
the appearance of objects, prior to the event rather than afterward. The game has to “look back
in time” to determine if these abilities trigger.