Originally Posted by
armus
3rd party search sites can find some (or a) codeshare, but when they send you to aa.com the website can’t find it.
Originally Posted by
USFlyerUS
The codeshare in question you're looking at might be limited to connections. For example, AA might place its code on AS's DFW-SEA flights but can only sell seats on that flight if connecting from SEA to somewhere else (since the codeshare approval limited codesharing on certain routes on which they compete directly). I'm not saying that's the case in your case, but it's one possibility.
I'm thinking it's more of an issue of stale data (especially if they used to codeshare) - the data I pulled from Cirium doesn't show any AA flight number on any of the flights, but does show KE, FI, TN, JL, etc. I also can't force any form of connection in SEA from another AA flight to SJC.