Join Date: Sep 2005
Location: HEL
Programs: AY Platinum, TK Elite, BT Executive, AA, BA, SK, DL, NT, WB + hotels
Posts: 10,258
If you book a J award, you will be rerouted in J even if flying another airline.
If you book a flight in paid Y and upgrade via vouchers/points, you can expect to be rerouted in Y.