I'm looking at a flight from SFO to FRA. Expert mode shows there are at least 9 seats available in the L fare class bucket; however, when I specify the L fare class in advanced search, the result shows that L fare class isn't available. In fact B is the only available fare class in economy:



I'm I missing something?

Further, I'm using the flight status tool is showing 53 out of 60 business seats have been booked already (meaning there should be 7 Business seats available.) Adding J, C, fares alone (from the screenshot above) would mean there are more than 7 Business seats available. Also, when I specify D fare class in advanced search, that fare class is not available.


My question is: why the discrepancy? How frequently does the inventory update?
As a side note, I was traveling with my SO recently and we were both on standby for CPU - but then i checked the UA app and it clearly showed business class was full. SO's sister had just purchased her economy ticket few hours before the trip; surprisingly she got upgraded right around the time we went to board our plane. We are all premier 1k.