QP, using your own words, I am going to add a clarifier within your sentence.
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person in the Bush Administration would have to be assisting in this cover-up."
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person in the New York Police Department would have to be assisting in this cover-up." (although common sense says this would have to be more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person in the New York Fire Department would have to be assisting in this cover-up." (although common sense says this would have to be more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person from the New York Port Authority would have to be assisting in this cover-up." (although common sense says this would have to be more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person in the media would have to be assisting in this cover-up." (although common sense says this would have to be more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person from the Pennsylvania rescue crew would have to be assisting in this cover-up." (although common sense says this would have to be more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person at the scene of the Pentagon would have to be assisting in this cover-up." (although common sense says this would have to be several more than one)
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person piloting Flight 93 would have to be assisting in this cover-up."
"If conspiracy theorists are correct that the government is covering up the events of 9/11, at least one person piloting Flight 11 would have to be assisting in this cover-up."
Having said all of that, perhaps the word “thousands” is not factual after all as my addition from these statements doesn't quite get into the 3 figures, much less 4, however likely it would have to be. If I changed the word “thousands” to “several” and admit I was wrong about the word "thousands," would that put a smile on your face?