For a domestic flight on AA, I am seeing a B fare available on ITA Matrix but not on AA.com. The fare difference is substantial. When I called AA reservations, and offered to give them the fare construction so they could look into this, the agent was polite but not helpful. I have not had this before with ITA Matrix -- usually if a fare is showing on Matrix, then it is available on the airlines' website. This is not a situation where the last seat in that fare bucket was suddenly sold (the fare continues to show as available on Matrix). Any ideas?