This is what I've been able to find out (for what's it worth) Ford calls it a PLATE (front fender apron access hole cover) and that's it ! Not much help there with that. The parts book shows :
1973 as 2 required -I can't go lower then '73 but they have a '71 part # - also they are shown as a triangle shape.
1974 and then '75 up show only one required - but with different part #s
My quess is they don't even know why they are there !
I'll just put mine in there and if I should ever have to remove it - I'll know why it's there