While the CPC percentage won't drop until they actually walk out the door on their release date, during the selections they act as if they were walking out the door that second. So the selections are based on both actual and projected numbers having one CPC taken away immediately. That's why during the selection, only one CPC will be allowed to be selected. Because it's the having one CPC taken away immediately from your actual number (23/28 down to 22/2
that will put you below the actual CPC national average.
But after the panel your actual number will stay the same until their actual release date and the projected number will have one taken away from it immediately. So even though your actual number won't change after the panel for at least 6-12 months when the lucky CPC to be selected actually leaves, (barring any hardships or retirements, etc) during selections they are taken away for pretend and stop you for being able to release any more CPC's.