Originally Posted by
anabolism
I don't think who issued the ticket or whose code is on it matters, because as I mentioned above, both AA and BA have published info on upgrades using Avios/miles that say it's OK to have codeshares (provides the flight is operated by any of AA/BA/IB and sold as any of AA/BA/IB). I suspect the problem is BA's non-published ban on upgrading DONEx tickets.
In my limited experience, I find that who issues the ticket does matter, as I have had no problem upgrading flights on a BA issued DONEn to first using Avios. Whenever I plan to upgrade DONEn BA segments to first I book the DONEn through BA. For example, most recently on a BA issued DONE3 I upgraded LHR-IAD to first and my upcoming PVG-LHR has also been upgraded to first, in both cases using Avios.
If there is a non-published ban, then your statement should probably be modified to read "the problem is BA's non-published ban on upgrading DONEx tickets
issued by other airlines".