I remember the show...."when a bell rings....".It is the concept that angels are “created “ on a constant basis. Many like to think of our guardian angel watching over us , thus the need for a constant increase in the number of angels.
Obviously people do not become angles. I doubt new ones are created, but I can't say none are. If new angles are created to watch over people then would not new demons need to be created to kerp up as well?