demon fender extensions on 73 duster fenders

I want to throw some input on the fender extensions. I believe it's the 1970 and maybe early '71 were fiberglass and then they went to that pot metal for the remaining '71 to '72.......but I could wrong. The reason I say this is I have fiberglass one's on my one '71 Demon that was built in late 1970, my '72 Demon has the metal one's. My other '71 I have no clue what it has.