The oath of the office for the President of the United States is included in Article Two of the U. S. Constitution. It is inconceivable that the President, and his advisors would not carry copies of the Constitution with them wherever they may go. Some coincidence indeed.
Give me a break, no one carried around the oath of office with them back in 63. When Sarah Hughes said to LBJ, "Sorry but I don't have the Oath of Office on me.", he handed her his copy and turned to the small crowd aboard AF1 and said jokingly, "If any of you speak of this, I'll deny it.", then he turned to his long-time friend, Texas congressman Albert Thomas and smiled, and Thomas returned a wink.
And if LBJ's 1st thought after the assassination was that it might have been a commie plot, then why didn't he have the nuclear football with him on AF1? Ans: because he knew the rooskies had nothing to do with it.