I suppose Jimmy is the most responsible for spreading that. What I can't understand is the fact that I don't see that too much (s)elected Board members have integrity above Jimmy's rumors threshold.
And the first part, as it wasn't well formatted initially: There is specific Board culture, transferred from generation to generation of Board members. The culture of siege, where the community is the archenemy. As Denny is repeating the same thing I heard from some of the previous Board members, while Jimmy is the only one with more than year and half of being in the Board, I suppose it's about Jimmy.
The second option is possibility that that culture is so strong, that it already assimilated almost everybody else up to the level of being able to transfer the mythology to Denny.
The third option is possibility that Jan-Bart and Stu have such powers, that they were able to indoctrinate Denny for six months of being together in the Board.
I think the first option is the most reasonable one.