Alex,

A confirmed North American Upgrade is different from the normal 500-mile certificates, and are generally only given to 1K's or for customer service problems.

You'll also see them referred to as HK49's on this board. They allow you to confirm your upgrade on any North American flight (regardless of distance) using one certificate, and you don't have to wait for the 100-hour window, it's confirmed when you book.

The "regular ones" are the 500-mile certificates that require you to go on the list until 100, 72 or 24 hours in advance require 1 certificate for every 500-miles of flight that you want to upgrade.