Yes, AP holders get a discount if they purchase multi-day tickets at the gate. Those discounts are 10-15% depending on what pass is used.
You seem to be confusing discounts on tickets with discounts on annual passes. There are no discounts on annual passes for non-Florida residents except for when they renew their pass for a subsequent year. You can only get a renewal discount if you had an annual pass the previous year.
You can, however, get discounts on tickets in many ways. You can get someone with an AP to purchase a ticket for you at the gate, you can purchase your ticket through the Universal site online, or you can purchase through a 3rd party like
Undercover Tourist.