How come some SS cars have "bumperettes" front and back and some don't. Was this another option or is there a "correct" bumper setup?

this was an additional cost option on most of the velles.

http://www.paw-talk.net/forums/images/smilies/may/yeahthat.gif

I've got them on my 69SS. I think they look good and add some detail to the bumpers, which I think look kind of plain without them. IMO