I was under the impression that any wild Tandemaus has a 1/25 chance of being one that is capable of evolving into the family of three form. Going through the built in encounter database, all of the listed Tandemaus show the same error message as previous if you change their species to a Maushold Family of 3 form and set their level to an acceptable value. I guess I'm just wondering if there's a hidden value that determines which form it will evolve to that isn't showing up on PKHeX, or if I'm just being dumb and it's something obvious I'm missing.