You're correct that the loan could still be floating, and of course, rates change every day.
That said, the lender must disclose when the rate is locked. Even if the rate went DOWN, a new disclosure would be needed and you would have to wait 3 days.
Unhappybuyer, this really is black and white. If the loan was locked, they cannot let you close within 3 days of disclosing different terms. If the loan was floating, then they would have to wait 3 days after they lock it. Either way, new disclosures are needed and a 3 day waiting period is needed.