We have booked a flight in business class on the new SEA to NRT route next November, using Alaska Miles. I have the JL confirmation code and used that to manage our booking and select seats. But I cannot enter our passport details; the website says it is not a direct JL booking so we cannot do it.

I thought it is a requirement that we do this in advance for international flights. Should I go through the "automatic check-in" form, say a month ahead of the flight, and enter it there? Or is it OK to wait and just show our passports at the airport? I am so used to doing this in advance, when we fly to Europe or South America.