Exact same issue, all Jan-Feb AC flights updated to 500 miles but not my UA flights. The AC explanation that the year goes Mar-Feb cant be right as they retroactively gave me 500 for my Jan-Feb AC flights. I was assuming that I dont get 500 for my 3 short haul UA flights. I have no status until Mar 1 then I became a E35K.

In summary, flew 8 shorthaul flights during Jan-Feb. 5 AC, 3 UA. Received increased mileage retroactively for the 5 AC flights but not the 3 UA flights.