I am traumogenic (trauma created/clinical DID) plural system. It is highly likely that I never had a "core personality" that I was born as and instead have always had either an infant mental state or multiple personalities. (During the time most babies begin to form a coherent personality, I formed several. It is possible that not every system forms like this but highly like I did)
Every time I've felt I was singular, I've experienced mental walls, amnesia and other DID symptoms. If someone could do a "I'm singular ama" that'd be cool because I have questions too. :)
It's an extremely common thing. In clinical literature, these are called persecutors and they are sentient. They can also be reformed. When reformed they tend to be some of the most protective members of the system. I actually don't have many conventional persecutors and they don't come out often. I mentioned this because I think it is the easiest area for an organizer to cause harm when trying to apply DID treatment strategies to organizing. Many survivors are pressured to let external family abusers back into their lives. With internal persecutors because they are inherently part of the psyche, you cannot and should not banish them. They also have a different capacity for harm than an external abuser. So, the whole "Awww...you're hurt, I'll forgive you" can sometimes work for an internal meeting but can potentially fatal when applied to external abusers. (Unfortunately, systems can also be abusers of external people and if a person is being abused by a system then the same protocols apply as being abused by a singular person)
man holy shit brains are so cool