What unlocks the authentic Sinistea log in the pokedex?

I have caught three Sinistea and I've encountered four, the fourth was a shiny accidentally knocked out because I was reading up on how rare a shiny authentic Sinistea is and mashing A

I have two Sinistea entries in my pokedex but none of the three Sinistea I have are incompatible with my cracked teapot

Please tell me you can't unlock the second entry from encounters alone, I wasn't even looking for shiny's when this shit happened I was just trying to catch an Indeedee to finish my dex for the area but now I'm filled with anxiety and despair