given that people without DID/OSDD consist of parts as well, I don't know why an alter/self state within someone with those disorders would somehow be expected to be a whole complete discrete piece

that being said OSDD is not a "thing" that is about whether you can or cannot experience XYZ. it's just a word we use for describing very roughly where along the spectrum of dissociative experiences someone is at

so like my answer is "why would it not be possible for an alter to have different parts of themselves when we expect that of non systems" and also (and this is very important) you have what you have. you experience what you experience. "having" or "not having" DID/OSDD does not mean your experiences are real/less real