Here is the response I got:
Peak Ticket
A 1-Day Peak Ticket is valid for one admission to one theme park on any Peak, Regular or Value season date.
Regular Ticket
A 1-Day Regular Ticket is valid for one admission to one theme park on any Regular or Value season date.
Value Ticket
A 1-Day Value Ticket is valid for one admission to one theme park on any Value season date.
Our 1-Day Peak, Regular and Value tickets must be used by December 31, 2017, but the amount paid for an unused, expired ticket may be applied towards the purchase of a new ticket at the current price, so long as the new ticket purchase price is equal to or greater than the amount paid for the original ticket.
Peak, Regular and Value validity dates continue to be added to the calendar from time to time, so please check back often. The dates assigned to each of these seasons and the number of days in each of these seasons may change from year to year.
Not valid for separately priced activities/events. No credit or refund will be given if a higher season ticket is used on a lower season date. Admission is subject to capacity closures and to other restrictions.
I'm asking for clarification of a couple of things.
1-Can a VALID ticket be upgraded (they only address expired)
2-When they mentioned 'dates continue to be added' does that mean that if I buy a ticket in advance that the price may change by the time that date arrives?