http://www.learnedhand.com/kerryunfit7.htm
From "Unfit for Command" Chapter 7
Quote:
On July 1, 1971, within days of Lo Duc Tho’s arrival, Madame Binh advanced a new seven-point proposal to end the war. Central to this plan was a cleverly crafted provision offering to set a date for the return of U.S. POWs in exchange for the Americans’ setting a date for complete, unilateral military withdrawal from Vietnam. In other words, America could have its POWs back only if we agreed that we lost, then surrendered, and then set a date to leave.
About one year earlier, two young Americans had also come to Paris, presumably for their honeymoon: John Kerry, a young, cleanshaven Navy war veteran, accompanied by his new wife, the former Julia Thorne, who could trace her lineage back to George Washington. But honeymooning was not John Kerry’s only reason for traveling to Paris. Kerry’s presidential campaign has now acknowledged that he “talked privately with a leading Communist representative” there.
End Quote
In the final analysis the FBI knew EXACTLY when Kerry and his first heiress were in Paris so it doesn't matter whether it was their honeymoon or not.
That trip occurred before Kerry became an object of interest to the FBI, to the best of my knowledge.