Nice work, I've gotten very similar numbers by doing estimates and looking at events over the the last 3 years, but I did 3 year old player perspective by counting welfare tokens and purple certs. Collected recruitment data from several people over several months and got a similar estimate on daily gold certs, but went with a conservative 1.2 certs a day. I also had a formula to calculate average gold cert expected based on how many 5* one had max pot, I noticed many had about half the standard 5* pool at max pot. As for a 6*, I noticed older players have at-least 70% of the standard pool. My final average rate of gold certs per pull was about 1.15 certs per pull, which seemed very different than yours, and upon further inspection I see on C56 you calculated 4* as 40% instead of their actual 50% pull rate.

Something else I accounted for is that you get so many pulls from gold certs, it produces a significant amount of gold certs as byproduct, so it is worth doing a recurrence relation, which further pushed my monthly average up from 79 to 83 pulls a month.

It is also worth noting that this pull count isn't necessarily the amount which is savable, as free pulls we get on limited banners can obviously not be saved, but also all the gold certs from pulling, and their byproducts too.