It is possible to move backward on the waitlist.
For example: An application in the Tier 1 preference group can move back in the waitlist if an application ahead of them has multiple children on their application, one of which was initially determined ineligible. If the parent appeals, and student is determined eligible, they are then placed together with the other students from the same household or family application. Therefore, that reinstated student would take a waitlist number alongside their siblings, and potentially ahead of other Tier 1 families.