The episode Odds and Ends Part 1 and 2 reveal that Ohlm is not known to be an agent on paper because there is no paperwork on him (as Oona states), yet is still considered an agent by Ms. O, because she puts him to work with agent Otto. It is never revealed how someone can be an agent and not an agent at the same time throughout the series. Conflicting information.
Ms. O and Otis are both expelled from Odd Squad because Ms. O helps Otis become an agent knowing fully well he used to be a villain. Yet, Ms. O is promoted to Big O after finding out that Ohlm is a villain, who she also lets in, and allows to assist agent Otto in the first season. She does not know that he is a villain in the first season, but through association could be considered a villain after finding out that he is a villain and allowing him into the squad. This is never explained.