I am on AA 137 on 9/15. If I query LHR-LAX I get C0. If I put in my whole itinerary, SMF-FCO with a stop at LHR, for the return LHR-LAX leg it says C4.

I called LA and asked for the C availability on that flight, and they said there was none. I asked them if it was a "married segment" issue, and they said no.

Please explain why EF has C0 and C4 for the same segment, and AA EXP says no C availability no matter how you cut it.