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A<---B some C
it can be inferred to C some A

but why can't
A some B <----C
have an inference of C some A

if the somes can be reversed why can't this be true. To me the book didn't offer a good explanation. Can anyone explain this?

From this information alone, we don't know for sure that C and A must overlap. For example, this hypothetical diagram is compatible with the second scenario you presented, but it contradicts the A some C inference.

A some B ---> C

I can validly infer that A some C. I know that some A's are B's and that every B is a C, so I must have A with some C's too.

A ---> B some C

I cannot validly infer that A some C. I know that every A is a B. But I only know that some B's are C's. For instance, lets say that there is one A in existence and that there are 50 B's in existence. I can have that single A be a B, yet have the other B's be with C's and not the single A.

A
BBBBBB
.....CCC