correct oval fenders have a metal tube for the headlight wires, also the shape of the bucket is distinct to oval and earlier fenders. also where the running board mounts there is a pronounced hump not found on later fenders. there are some more differences such as a more pronounced curve over the headlight , but the first 3 i listed should tell you at a glance what you are looking at.
some pics
this pic shows the metal tube for headlight wires. also the shape of the rear of the headlight bucket, later fenders have two small indentations at the top and bottom of that crease in the centre of the bucket
this one shows the flare at the bottom rear edge where it meets the running board. later fenders don`t have this flare
pic of later non oval fender, in headlight bucket you can just about see the indentations in the rear of the bucket