In The Giver, why was Jonas' number skipped during the assignment ceremony?

Jonas's assignment was unique and special; it wasn't a typical job like his classmates were getting.  They skipped him because they needed to explain a little bit more about his job, and because it was a somewhat historic event since they only choose a new Receiver once in a lifetime or so.  When Jonas got his assignment, they apologized for confusing him, and explained that he was being given a very special job.  They talked about how he had been specifically chosen for this job because they knew his talents and personality would be a good match for it, etc.  So his assignment took a little longer than the others, and required a little more explanation.  Instead of just throwing it in with the rest of the assignments, they skipped his number and kept his assignment until the end.