Puthujjana wrote: “How can a puthujjana know who is an Ariya? As monastic is not allow to reveal their attainment to a lay puthujjana.”
That is not correct. There are several suttas that clearly state one could declare the magga phala attainments. One is the Maha Parinibbana Sutta (DN 16). It is at the end of the following section of this long sutta, specifically regarding the Sotapanna stage:
https://legacy.suttacentral.net/en/dn16#14
Also, there was a long discussion on this topic sometime back:
“Four Conditions for Attaining Sōtapanna Magga/Phala“