Originally Posted by
xliioper
$872 fare is a LNN4AQR1 fare which books into R. $623 fare is a GNX8AQI1 fare which books into I (as you noted). The fare basis codes can be found at end of booking process at fare rules link and can be looked up on ExpertFlyer. ExpertFlyer can also tell you what it sees for bucket availability on flights with Flight Availability search.
I always forget to check that before purchase and I don't see any way to pull up the fare (or FF earnings) after it's booked. I let my EF subscription lapse when I wasn't flying last year, but it might be time to renew.
Originally Posted by
xliioper
Looks like Google Flights may not be looking at married segment inventory (or perhaps it has stale cached inventory). ITA Matrix gets it correct with one-way search (showing R fare), but Google Flights does not. Generally, airline sites will do a final check for married segment inventory before allowing you to book (I know Delta's site does). They will dutifully pull up any published fare with API interface without checking inventory first. It's only when you checkout where they should do a final inventory check.
I was able to purchase the fare and it did get ticketed at the lower price. I know GF does sometimes price fares as separate tickets which may be the case here. I'm just surprise that the AA website allowed it and didn't reprice it at the higher fare.