Technically, the language pasted would be applicable if you bought your ticket and NWA lowered the price more than $5 on the same day. Otherwise, it would not count. Basically, they put these guarantees in to get people back to their site. When fares first came online there were situations where you'd find diff fares at diff sites. They want to you find at least as good a price on CO/NWA/whatever airline.com as they already pay for the site and don't have to pay anyone a booking fee.