Regarding the quotation that Akvan gave from the post, I just revised that sentence to make it more precise: “Thus when one gets into the Sōtapanna magga citta, for example, one receives the Sōtapanna phala in the very next citta,..”.
I also added #3 from my post above to that post (new #2) to make it more clear ( https://puredhamma.net/three-levels-of-practice/sotapanna-stage-of-nibbana/sotapanna-anugami-and-sotapanna/ ):
The citta vithi for a magga phala is discussed at the end of the post, “Citta Vithi – Processing of Sense Inputs“:
B B B “BC BU MD P U A G Pa Fr Fr” B B B
In other words, a Sotapanna Anugami is getting closer to the “change of lineage” or G. The earlier stages of P, U, A, may be reached gradually. Once that level of comprehension is complete, one makes that transition (G), completes the lokottara kamma, and immediately receives the phala.
Akvan said:” If a person who is striving to comprehend thilakkana and working towards becoming a sotapanna is a sotapanna anugami shouldn’t a person who has already reached the sotapanna stage automatically become a sakadagami anugami?”
That is essentially correct. But technically, a Sotapanna is not called a “Sakadagami Anugami” unless he/she is making an effort to get to the Sakadagami stage.
Yes. The explanation of y not is correct.