Thank you for your thorough explanation! It was a smart move to realize only CD species were spawning during the major event (even the nest pool was replaced to reflect that) and only those 6 or 5 were spawning during the inner CDs. I was wondering if you also worked with the possibility of weather boosted spawn rates for Porygon and Rhyhorn. We don't really know how much is generally increased but perhaps working to a few models would be interesting to rule out weather boost effects in spawn rates during exclusive events like CD and GO Fest for example.
In this post, I focused on shiny rates because changes in species following ruler models like yours have been reported before. I think it started with the realization that the nest pool was organized by pokedex order and that changes in species could be predicted when an event altered the nest pool. u/Zyxwgh talks about it in this post.
Nest masking was the next step to approach the whole spawn table as being ordered by pokedex. We've seen numerous complaint posts about Pikachu and other early spawns not being available during certain events in nest areas. Here are some examples: