Spirit pilots CANNOT have their vacations cancelled. They can, however, be postponed and they are rolled over to the next year if the pilot elects not to trade into an open period. There are no caps when a vacation is rolled over and no pilot may have his vacation postponed for more than 2 years.

F9 has no such protections.

F9 Pilots top out at 4 periods.
Spirit pilots top out at 5 periods.