Ok, I understand now. It should work in MSFS as well but:
- Your airplane must have some airline codes in the atc_parking_codes of its aircraft.cfg
- The airport must have some parking codes in its parking
- If you are using the SU10 Navdata API, even if the scenery does have airline codes, they won't be returned by the API so, GSX can't read them from the scenery, unless you add them to the GSX airport profile.