Good question. Good luck getting a straight answer.
We know this much, he was there and he stayed.
November 12 - 15, 1971 -- the VVAW leadership meets in Kansas City. Fearing surveillance by authorities, the group relocates the meeting to another building. They debate, then vote down a plan to assassinate several pro-war U.S. Senators. Despite John Kerry's claim to have left the VVAW before this event, several witnesses, meeting minutes and FBI records eventually place Kerry at the Kansas City meeting. WinterSoldierTimeline
paperlessarchives: John Kerry CIA files *Note: CIA, not FBI