Yes the yq would be for all segments as the way the system works you select all flt segments. The system then quotes the itinerary as a whole. Thats the way its displayed on the ticket as one value for fare and one for 'tax' which would include yq and then these values are the total for the itinerary rather than being split per flight.
***** all opinions are my own and dont represent those of ba or iag*******