I've found old hub caps over the years as well , there is a lot of them waiting to be found , although not really sure how many older ones are still out there . some of the one's I've found aren't that old
generally hubcaps earlier than the fifties weren't that big they tended just to cover the center of the wheel where the lug nuts are, anything that has an air valve hole in it is generally 1950 or later.......Andy