Bus Passenger seating requires identification of the Seat Manufacturer to ensure you obtain the right seatbelt for the seat.
In general, facing towards the Front of the bus seating is identified as: LH Side LH Outer, LH Inner. RH Side RH Outer, RH Inner.
Also determine how a seatbelt is configured eg. belt runs from LH shoulder to RH hip (LH2RH) etc would provide a greater degree of accuracy when choosing a seatbelt assembly.
...So 'the seat by the window' is not the best way to identify which seatbelt you need.