Although a visa wasn't required, I had a whole ship's crew, all travelling on seaman's airfare tickets, carrying Seaman's books and letters from the vessel's handling agents at their destination, refused boarding by a dim check-in desk worker AND her supervisor because they didn't have a visa. I parked them up overnight at an airport hotel and rebooked them on another airline the next day that didn't have ignoramuses working the desks.
Some supervisors are worse than those they are supervising. They are mostly subcontractors and not airline employees, and work for several airlines during the day all serving different destinations and can't be arsed checking the rules when forced to make a (wrong) decision.