wow so sorry it has been so long in my reply... health issues with my mom and then with me and now getting close to my daughter's wedding in 2 weeks so i have not been very active here...
but to answer you YES you can ALWAYS upgrade your tickets to an annual pass AS LONG AS you have at least 1 DAY left on them and if you do upgrade the FULL value of your entire ticket will be applied to the cost of the annual pass.... BUT the annual pass will be dated starting from the first date you used your other tickets.... this is a GREAT option if you are coming back at least once in the next year and if you intend to make more than one trips in the next year then it is a near must
but to answer you YES you can ALWAYS upgrade your tickets to an annual pass AS LONG AS you have at least 1 DAY left on them and if you do upgrade the FULL value of your entire ticket will be applied to the cost of the annual pass.... BUT the annual pass will be dated starting from the first date you used your other tickets.... this is a GREAT option if you are coming back at least once in the next year and if you intend to make more than one trips in the next year then it is a near must