Will user A see my post? http://lh3.googleusercontent.com/-RIL_CvjOmVY/ThQKTNckBYI/AA...
Also if you send something to one circle and then add someone to that circle later, they get to see everything sent to that circle.
e.g: You and your friends are throwing a surprise party for one circle-member's birthday.
Nevermind: just noticed that that only applies to posts you share publically.
They could also just tell person A or repost it if there wasn't a share button, though. Just use good sense.