It does not know when it switches usually till later because it has so many fragments & shards and bes accustomed to being taken over by other entities not part of the vessel itself. Generally it only recognizes specific switching when it occurs with one of the primary selves or self-parts, one of those whats got a name or number distinct from the multitude of fragments. Otherwise the fragments just rotate in the Vortex and shift in & out of forefront slot according to the current velocity of the Vortex (which bes regulated by Leviathan).

that being said ... when all this first started coming to light its primary core/key self part had been "killed" (so we thought) by the emergence of the diametric dualist Twins in succession at ages 16 and 18 respectively (whose origins date to the original splitting trauma at age 3, an event Mal calls "Crack-the-Sky"). She did not resurface until a period of intense therapy in 1994 -- so for 13 years we all just thought she'd died to make way for the first Twin's "spiritual rebirth".

so yeah they may disappear from all access & view but that does NOT mean they bes gone forever. take comfort in this Manda.