As I understand (maybe I´m mistaken), if sometimes perpetual licence holder "brake" maintenance, all other deals become kind of "subscriptions" for him. So, perpetual licence of XP will "freeze" to last day of maintenance expiration date and could not be "updated" by buing maintenance in the future. Only way to have perpetual licence of XP "actual" is not "brake" maintenance line...
(if understood correctly of course)