I flew SEA-HNL-ITO. Ticket was booked on NW website, all flight numbers were NW, but the HNL-ITO-HNL flights were code-share operated by HA.

I'm Skyteam Platinum. On the outbound, no charge for my checked bags.

On the return, HA told me there was a $20 charge per checked bag.

??? I was lucky. My daughter was with me (not flying), so she just took the two bags back home with her. But this made me realize how complicated the whole 'checked bag charge' thing can be. To be honest, I've never paid too much attention to code-share arrangements as long as my FF# was entered and credited correctly. Now I'm going to have to pay attention to the operating carrier's rules.