Why is a barcode called a “proof of purchase” even though it’s there before you purchase it and remains whether you actually purchased the item or not?

Question

Basically, the title. Why is a barcode called a proof of purchase, even though it’s usually printed on the item and is still there even if you have stolen said item?

In: Economics

Answer 1

Old things that used to use this in contests and rebates had you mail in a cut of of that barcode from the box.

You’re right it could be that you stole it, but its more proof than you just sending a letter saying ‘I bought product X, give me a $50 rebate’

Actual ‘proof of purchase’ like a receipt would have a bunch of other things on it, and also doesn’t really prove it as you could have then returned the item.