It is always recommended to enter all the traveller info at booking or soon after and before airport check in for international travel for a number of reasons.

Requirements and regulations vary from country to country depending on citizenship/resident status and visa requirements. Just makes things smoother if the check in agent does not have to type in anything (avoids mistakes) or misinterprets visa requirements (has happened) and requires calling a supervisor, etc.

Some airlines allow this to be entered during online checkin when it opens before departure date and without it may not allow check in, and/or not allow selection of seats (can be a problem if you need to do this quickly as soon as OCI opens to grab a good seat), etc. Better airlines even pre-verify a few days ahead and send mail about required documents, etc. Very useful if you are flying to a new destination with document requirements or for inexperienced travellers.

While passport number, in theory, can wait until last minute, US travellers with Global Entry will need to have entered their KTN at least a few days before so they can get the Pre TSA check on their BPs. Have no idea where this would be done on JAL website or app if booked via JAL.

All these are part of the traveller information forms that airlines (except perhaps JAL) and travel sites allow as SOP and people who have grown used to these as a habit might certainly pull their hair out on encountering JAL IT inadequacies.