Your flight probably had an "ineligible flight number." It happened to me on a ORD-MSP flight, and AS really gave me the run around, telling me they don't partner with Republic, the plane wasn't operated by AAL etc.

So, call in to customer care and explain USAir didn't operate DFW-SJC when you flew. Some of the DFW-SJC flights carry AS code shares. If yours had one, you shouldn't have any issue getting credit. If not, it might be a little more difficult, but you should get credit. In my case, they had to manually enter the flight as an Alaska flight, with the codeshare flight #, before the system took it. Took 45 minutes...all for 500 miles.