That appears to be true. I have two LATAM bookings, one issued by BA, the other by AS. It's an LA flight number and LA operated (issued by AS), but the website still doesn't allow any upgrade.




It's giving a "wrong" reason though, since marketing carrier isn't the issue - ticket issuer is.

At least seat reservation is working, and the website is already showing 2x 23 kg instead of just 1x 23 kg bag allowance.