One easy way to tell if it's a re-chrome is that they are thinner (the chrome shops have to grind off the old chrome) and they usually leave the washers that they weld onto the backside to support the bumper when they dip it. I have never seen a "wavy" bumper that wasn't damaged at some point.
Hans
The bumper is off a Malibu but it’s the same part number for el Camino. It came with all the original internals, centerbrace etc, the bolts were rusted in and I had to cut them out Indicating it’s never been taken apart at least not in a long time. It also had the original impact strip in mint condition. I looked at some other pics of malibus and noticed some have this waviness around the edges as well. Take this picture from OD showtime for example, this is a Malibu he has and it has the waves on the edges as well. I think some just came like this. That seems more likely than all these bumpers were hit on both sides and then restriaghtened. It’s also only on the malibus that I find others with wavy edges like mine, and it’s always the year 1983 Malibu whenever I find one with the wavy edges and that’s what my bumper came from, I think it’s a factory error all things considered
Also this bumper has never been rechromed. And that’s obvious in person, it’s the original 40 year old chrome and the backside has no peen marks or anything out of the ordinary, when I was asking if it has been straightened I was referring to method that do not require rechrome like chain straighten because I can tell it’s clearly never been rechromed