I would assume (and you know what that means) that the last two years would be used instead of resetting every two years.
Think about how absurd the SF currently is. We don't know if Mater Dei has achieved enough success points to be bumped up to 3A. Despite being a runner-up in 2021 and winning 2022, if they lose their regional game this fall, they will remain in 2A. A rolling success factor puts them in 3A for the next two years, regardless of what they do this fall.