I've been told the same thing by some agents, yet one of the price drops we processed today was the second reprice for that booking. It's irrelevant in most cases, since I can just make a new booking at a lower price and cancel the original at any time prior to final payment. If the price drops, I'm locking it in before they change their minds.
That said, we can't rule out the possibility that somebody at NCL got the cart before the horse this time and the prices will be higher very soon (e.g. midnight eastern tonight).