The other day here, I said that the Washington D.C. Fire Department had issued an estimate of 60,000-70,000 people for the 9/12 rally on the National Mall. A lot of sources were reporting that and it turns out that's wrong, too. The Fire Department says they never issued any sort of estimate.
Apparently, there is no such thing as an official estimate of crowd sizes in Washington, at least from any official department. Some used to issue such estimates but the organizers of events always got mad that the reports were lower than they claimed, and some even sued or threatened to sue. The press issues estimates but reporters don't usually have a lot of experience in this area, or access to data like police or transit reports. And of course, this is America where the media is always a pack of lying, biased weasels whenever they say something you don't want to believe is true.
FreedomWorks, a group which is described as the main organizer of the rally, has halved its original claim from 1.5 million to between 600,000 and 800,000. Some of their followers may believe that, some may stick with the original 1.5 million, and it doesn't matter that even some right-wing press said "tens of thousands." These folks will never believe that Obama isn't a lying, Kenyan-born Nazi who's planning to have his secret army throw political opponents into concentration camps. They might as well believe there were 700,000 of themselves there that day.