Originally Posted by furnace

Answering my own question in case anybody else ends up in a similar situation...

It took some time and work but the gate agent was able to send the bags all the way through. I saw some chatter elsewhere that OW has stopped interlining baggage in this way but it sure didn't seem to bother the AS agent. They even linked the JL and AS itineraries so they even show up now as legs on the same trip now in the Alaska app (although the JL itineraries shows up again with its own PNR right below). The tags were completely correct, at least. I suppose the moment of truth is at the carousel in NRT.

In terms of my question about weight: I'm not 100% sure since since were under 50lbs for each of the bags (the AS limit) but my strong sense coming away from the interaction is that we would have deal with the AS limit on bag size since our first leg was on AS.