Earlier this year I booked a LAX-LHR-VIE flight in Y and used a SWU to upgrade to J. Of course the BA flight from LHR-VIE was economy. But today I called AA and after a bit they confirmed my SWU was good for the BA segment too since they’re for up to 3 segments, def a much nicer perk
When Iberia does this I’ll be even happier, since I tend to take business trips with them to SA