something that i recently internalized and that i think every single being that is plural questioning or newly plural needs to hear, from someone who's struggled with this for a while:
There is no plural police that will ticket or arrest you for calling something a headmate when it turns out not to be, or being plural "the wrong way", and anyone pretending to be such a thing does not deserve even a MILLISECOND of your attention or consideration.
from my own personal experience, it's very difficult to distinguish between imagining a headmate saying something, and them actually saying it.
this has, for years, led me to swap back and forth between calling myself plural and a singlet, believing that my headmate at the time wasn't an actual being, simply a persistent intrusive thought about having a headmate. i believed that i somehow wasn't "plural enough" because my headmates all felt like, in some way, part of 'me' and not their own cleanly divided entities.
i am here to tell you that even if that was the case, even if i was making all of it up, even if i had simply created them from my imagination and believed they were real, that i would have been right to call myself plural. personally, it's my belief that assuming you're plural is likely better in any uncertain cases; treating that thing in your head like it's a real consciousness, even if it isn't, is always the preferred option when the alternative is even potentially denying someone's very existence.