Brian, the foundation is not the "source of authority" on what did or didn't happen years before they existed. The sources of authority would be those people who were actually present and involved in the situation.
I'm sure that the entire company wasn't solely Jimmy and Larry. There are probably others who were employees or whatever who could also be interviewed on the matter.
As well there are archives of what Jimmy and Larry did or didn't say, and when and to whom. The foundation really is irrelevant in writing the "History of Wikipedia: The First Two Years". They aren't even a primary source.
Will Johnson