I am planning the following itinerary: XXX (US) - American Airlines - YYY (US) - Japan Airlines - HND - Japan Airlines - KIX.

The first 2 segments (XXX-YYY-HND) are ticketed separately from the final segment (HND-KIX). I had initially understood that if I tried to check my bag at XXX all the way to KIX, the American Airlines representative would likely say no, however that's fine since my bag can be carried on.

Then I saw that despite the OneWorld rule change taking away baggage through check on separate tickets, Japan Airlines still endeavors to do this whenever possible:

https://www.jal.co.jp/en/info/inter/161003.html

Does this mean that if I approach the JL check-in representative at YYY (the international departure point), they would be more likely to check the bag through to KIX?

Edit: not sure if class of service matters - first 2 segments in domestic first / JL business; last segment to KIX still pending booking but could be economy or business.