@silver fox well, logically, I'd doubt that they joined a trainer organization before they even caught their first Pokemon. Plus, why not just RP them joining? Its a fast process that tou can finish either in the entirety of a post or just a single sentence or two depending on how you do it.
Mostly just state that the character is joining an organization in-character and tag the person who owns the organization.
Did that make sense?
Yup I kinda figured. So in order to join, does one walk to headquarters and fill out a form, or something with their pokedex or talk with a receptionist?