As you know, Sr. Rater bullets are pretty important as it determines to "promote now", "with peers", whatever and of course the 1-1, 2-1, etc.
I would ask what kind of relationship do you and your CO have? Maybe he likes you or dislikes you and wants to put his two cents in.
Maybe he doesn't want to put the new Commander who doesn't know you in a position to Sr. Rate you because in reality how well can you really rate someone within a couple months time span.
Me personnally, I really wouldn't care about getting a 10 COR over an annual unless I had something brewing up and I really wanted it on that NCOER to make it stronger, like completing a course, school or earning a degree.
I don't see the big deal, why is it an issue?