On the 3DS, from the Virtual Console games, if I transfer a Kanto Pokémon from RBY to Sun/Moon it should appear that is from Kanto. If I transfer one from GSC to Sun/Moon it will appear that is from Johto, but if I send one Pokémon from Red to Gold, will it still say that is from Kanto? (same if I send a Pokémon from Johto to Kanto, GSC to RBY).
I've been able to try this for you. So I caught a Pidgey in Pokémon Red, I then transferred this to Pokémon Silver, then using the Poké Transporter / Bank I was able to move it to Moon (pictures below). Unfortunately it doesn't say what region it was from, exactly.
Of course one of the benefits of transporting Pokémon to Sun/Moon or Ultra Sun/Ultra Moon is they instantly get 3 max IVs and Hidden Ability.
Apologies for the low quality pictures, I was using my mobile phone and 3DS, and also for no picture of Red.
Pidgey named STACKEXCH! caught in Red placed in Box 1 in Silver.
And finally the summary page, which unfortunately doesn't say what region it came from, only that "Seems to have traveled across both space and time to reach you from a distant land in the good old days" The Gameboy icon indicates it was from Gen 1/2 but isn't specific.