Ya. I know it's all digital distribution now. I meant "attached to the print" as it was part of the film. It's part of the contracts with the theaters in the US. They can be fined or sanctioned from getting certain films from a distributor if they violate those contracts.
If something went missing (like a trailer) in the days when actual prints were sent to theaters, it was usually down to someone splicing it out and taking it home or selling it to a collector. It's not super frequent as the guy who cut the prints together, the projectionist, was generally the one union job in US theaters.
When I was a film major, we were still required to shoot on film. All film splicing is low tech. We generally used tape instead of glue but the process is the same.