Ignorance is no excuse. These are not Novice or Atom coaches. They know the rules, and had 5 days since the prior weekend to ask for clarification if they were not sure. If it was the same day and they had not noticed what was on the sheet from the prior game then you almost understand how that might happen, but this is quite different.
As for the opposition I doubt that they would have known that one of the Brampton players had received a suspension from a game a week prior.