In the air-travel world, a lot of seemingly-random limitations on systems that interface with reservations comes from the fact that they were originally built with telephone interfaces intended for use only by trained staff.
Every few years, for example, someone digs up and reposts one of the articles explaining why some airlines didn't allow 'Q' and 'Z' in account passwords (they were passing things directly through to SABRE on the backend, and so only allowed letters that could be "dialed" on the 1960s rotary phones SABRE was designed to interface with).
Every few years, for example, someone digs up and reposts one of the articles explaining why some airlines didn't allow 'Q' and 'Z' in account passwords (they were passing things directly through to SABRE on the backend, and so only allowed letters that could be "dialed" on the 1960s rotary phones SABRE was designed to interface with).