The only 71 that would have bumper slots is a very, late almost 72 model. Do you have a slotted bumper? If so does it have the notches for the rubber corner fillers? The one late 71 bumper I saw had both. The 72 bumpers I have seen have the slots and does not have the notches for the rubber corners. I wish I had more documentation on the 72's. It is more than a 90% chance that your car came without the slots.
Here are a couple I happen to have on my iPad that show the details. I can take some better ones when I'm at my shop next if needed.
these are better full size on my iPad, I can see I'll have to take some better shots.
Sometimes I wish these cars could talk. That's what I wanted to know as I have 2 loose '70/1 bumpers and now I know I need to keep the better of the two for eventual replacement onto this car. Thanks again guys and keep posting here what you have on you're '71s and the build date as reference for all who might like to know.