Most were a rubbery plastic material called Endura. It was flexible and meant to absorb minor bumps and keep its shape. Of course, years later it's brittle and shrunken. I've seen similar repairs on slightly later years where flexible plastic or even flat aluminium panel was riveted onto a ground back edge, then filled over with flexible filler. It's not perfect but can save an otherwise ruined nose. It just needs to be flexible too as the nose flops about especially during installation, along with heating and cooling cycles. I'm not sure how well it repairs with fibreglass patching or any sort of plastic welding, perhaps melting a mesh across cracks before a fill coat.
