Hello there, regarding your question about RNG in Discuss my Pokémon, no, you don't need to have captured a wild shiny for RNG. But, you can only search for ivs this way, not for shininess. The "needing a wild shiny for RNG" thing was because a wild shiny was the best way to find your secret id which is in turn needed to RNG for shiny pokémon. You see, in the games shininess is determined solely on the ID and SID (secret ID), but now there are easier ways to find SIDs. Hope this was helpful