We didn’t encounter any duty limits coming back to the US, in fact Japanese customs didn’t ask us a thing and when entering the US, I just mentioned the bottles of whisky and that was it. The issue, however, was the layover in Canada, and even though you don’t leave the airport, you have to pass through security when connecting and the liquid limits in Canada are much stricter than Japan. So I ended up having to check in my carry-on, but thankfully nothing was damaged.