Yes there are indeed two waitlists. "PA" and "PB"..which stand for priority A and priority B. If you are 1K you typically get to be placed on the PA list which must clear out before any PB's are upgraded. Although there's plenty of anecdotal evidence that agents have the leeway of putting anyone on the the PA waitlist (regardless of status) if they choose to.

When requesting upgrades yourself online.. 1K's and requests made from a 1K's account go on PA.. all others will go on PB.