Alaska has somewhat improved their transparency, I recall having to go to each partner page and look up flight ranges that were specified as valid. Now there is this Atmos Rewards™ eligible flight ranges - Alaska Airlines

Many of the bookings we are talking about here include overwater flights that are codeshares and at least some do not appear to be in the ranges of those where AS will give credit -- thankfully BA6001 which I have booked does ;-) When we booked the EI plated AY fares last year, there were lots of options but they all included sticking in a mix of AY coded but other OW partner operated flight. So something like an AY coded BA flight on LHR-LAX, which was sold as AY5459. That is NOT on the Alaska chart now (and it wasn't then) and they initially declined credit. It was a cheap enough trip (and a really fun one!) so I did not additionally push back. Eventually we made a second appeal and credit was received. But I wouldn't rely on that for EI operated flights, we essentially pointed out that these were all OW partners and as passengers we did not care who put their flight number on it, we could see the name of the partner (BA) on the side of the plane. Surprisingly, it would work for some EI operated flights, the IB coded EI fligtht from YTO-DUB that I had posted was IB6054, and what do you know, that is within the ranges that AS now provides (IB 0001–9999). Actually, to my reading of it, that is every single IB marketed flight out there, so the concern wont really apply with IB codes. But AS is really stingy with AY, and has only now added the more extensive listing of BA codes.