Hey G$, if the bottom vents were replaced they would of had to be reattached with a nut and bolt. Looks like the original rivets in the photo
Likely, but since we can not see the bottom, the bolt head may be in the bowl. I almost thought I saw a notch in the pan head for a screwdriver. I have also seen people reattach vents using rivets. Anyway, probably moot, because based on the tab slots I really think it is a 70s bowl anyway.
But god, that lid. I love it!