Question regarding most/some statements

321raymoney123

https://7sage.com/lesson/advanced-valid-forms-review/

We have B-most->Z which implies two inferences B-most->C and B-most->/O. When you combine B-most->Z with B-most->/P, that gives you the inference /P some Z. But can you also then take the two previous inferences, B-most->C and B-most->/O, in combination with B-most->/P to create to additional inferences, /P some C and /P some /O, respectively? If those last two inferences are not valid inferences, then why are they not? I ask because in the comments on the lesson, someone stated that you can infer /P some Z but NOT /P some C and /P some /O, which makes zero sense to me.