I’m sorry but the Norwegian aircraft that operated for TUI used the flights designator BY. Agreed they operated from South as did all Norwegian flights. BA and VS swapped terminals because the VS pattern complimented the EZY pattern. Also at the time the BA short haul wave had expanded significantly up to 2017.
You know for certain that passengers will departing from on terminal and arriving at another? I suspect that most holidaymakers will be on 7 or 14 night trips in peak summer. Even if terminals are different it’s not that much of a bother at Gatwick.
When the initial swap took place on 2017 EasyJet had 19 fewer aircraft based at Gatwick.