Fender Pentastar

OK,I know this may sound like a stupid question but were all of the pentastars plastic?I have seen plastic stars and metal ones alike,so which ones were the proper application on a 71 a-body?I have been told that all were metal until late 1972 then they were plastic,but i can't find any imfo to verify this.Does anybody know the correct application for this,or am i wrong completely?Thanks