My theory on how MiY will be revealed

Okay so assuming that MiY collects teeth to shapeshift is true, then for him to transform into Sofia he must have taken her teeth at some point of time and killed her. Now if Sofia was from some decades ago possibly from the previous cycle and she's dead now, then Acosta finds Sofia in an old picture then her suspicions arise on Sofia's reappearance now after her death and then Acosta with Boyd or Tabitha or anyone else puts two and two together to reveal Sofia