I think it depends what your ticket actually looks like. If it's identical to the regular park admission tickets, you may be credited with the full value of the ticket, even if it was purchased at a discount. That's what happened with us. We'd gotten our tickets from ticketsatwork.com, discounted about 10%. Exchanged the voucher at the ticket booth, got standard park tickets. When we upgraded them to APs, we were given full value for them, because there was nothing on the tickets that indicated that they'd been discounted. Saved us about $100. I wouldn't count on that happening, but I'm sure we are not the only ones who've ever experienced that.