FAQ

While multiplex personhood/Plurality usually does feature shared memories, each ego may use the brain a bit differently, connect and associate memories and their individual pieces differently, have mental blocks against remembering certain things, etc.

In the case of Plural folks - "systems" - with DID, this can be astronomically more profound and quarantines of memory and cognition can result in "multi-consciousness". Systemic total switching amnesia isn't common, but it can happen in extreme trauma cases.

Ultimately, John and Jonathan's condition is a fictionalized variant of the Plural neurotype and doesn't conform to all the expectations of real-world Plurality and Plural disorders.