Here was Beth's answer I received in May
1. For the nwa.com check-in and self-service (SSD) if the Elite member (SSR ELITE in Gfax) is not already upgraded, we will offer to upgrade to First class. If we are not able to upgrade, then the passenger is placed on the PPL with the correct elite tier status.
2. The Worldspan PPL process puts passengers on the waitlist based on the time of the check-in and within type/Class. Examples of Types are Platinum, Gold, Silver, etc...) So first on within a Type/Class will stay on the top of that grouping. But since there are multiple groupings a members position on the /SPAN>PPL can and often will change. For example a -H is a confirmed psgr on the =light and they go to the top of the list, followed by -X who are mishandled psgrs, etc.
3. There isn't a history to the PPL and everything is kept in Time order (last column) of the last update.