Just did a quick search on the X Envelope. Seems to fit more and more. Here is what one article had:
"On May 14, 1973
, Walt W. Rostow, who had been national security adviser during some of the darkest days of the Vietnam War, typed a three-page “memorandum for the record” summarizing a secret file that his former boss, President Lyndon Johnson, had amassed on what may have been Richard Nixon’s dirtiest trick, the sabotaging of Vietnam peace talks to win the 1968 election."
Here is the website:
The main thing here is the year! 1973! Didn't someone else indicate that the year in the past for X-men DOFP will be 1973?