I have been trying to book a flight from Providence to LAX via Atlanta. According to Expert Flyer, There are U seats available on most of the flights out of Atlanta to LAX. Yet when I put those flights into Delta's website using the multi-city search, it prices them out as K. I did a more simple search, and while it showed me options for U class through other cities, it told me the flight combination I was looking for was pricing at K. Is it possible that even though Expert Flyer shows 9U seats available, they really aren't?

P.S. My trip is PVD to ATL on My 3rd, returning the 5th through CVG.