Can you please tell me if I misunderstood something? If I understood it right, it was said in the First London Stream that it can sometimes happen that you can encounter two different Electro Star Class 375/377/387 coupled together as one unit.
You are mostly correct, if you you have the SEHS layer then sometimes there will be a Class 377 & 375 coupled together as an 8 car train, this is because South Eastern have leased 3 Class 377's from Southern IRL Edit: the Gatwick Express 387 wont appear in this train, Joe has also put the Southern trains as the correct numbers as in real life
Also worth noting that later in the day/evenings you will see GX 387’s running Southern Services to Brighton.
