The charge relates to Boro only, but the tribunal can consider any evidence it thinks relevant, and decide the importance and credibility of that against the charges.
I've said above that the tribunal is adversarial cum inquisitorial, meaning it referees the scrap between us and the EFL, but also digs in as it needs to in order to get the information it thinks it needs. It's hard to see what other clubs could say that's relevant, but it's not beyond belief that they've had a say.