I only remember the A-B-C variety, no numbers. It would be fun to have one or two to show how it used to be done, but I do not miss them at all. The gate lice aspect with that system was terrible, and trying to get seats together was even more of a challenge, or perhaps we were just less assertive when we were less experienced. Looking at those plastic BPs from today's perspective, what a great vector of bacteria/virus from one person to another. I feel sure that the boarding passes were never cleaned, just used until the lettering had worn or faded off, and then discarded. In this COVID era, not an optimum arrangement. Definitely museum pieces now, along with such things as the ticket dater stamp which the counter agent used to diligently stamp each paper ticket sold. The process has come a long way.