The reason for this is to avoid any possible confusion about which June 24th the ticket is for. The reason it's not 364 days is to give the airline time to clear recent flights out of its database. (That's not be a source of confusion in booking tickets, since one is not likely to want a seat on yesterday's flight, but it can be with other types of inquiries.) They don't need a month to do that, of course, but 331 days is a hold-over from earlier record-keeping methods.