It is not uncommon these days for promotional fares with a fixed latest ticketing date. Instead of having a published policy for free changes that requires manual adjustments on fares with change fees, having fares free changes in the fare rules allow automated processes. Some other airlines put specific free changes for ticketing before 31MAY (example date) and usual change fee for other ticketing dates. However, when a ticket is reissued following a change, I don't know if the rule applies based on original ticketing date or based on actual ticketing date of the reissued ticket.