While trying to work out what was happening with the Wivelsfield-Lewes connector on BML and ECW I realised that all services going north on the connector were prefixed #1F[odd number] and all going south were numbered #1F[even number]. This numbering is consistent across both BML and ECW, and if you find a service with the same number on both routes it is the same service! I was seriously impressed to discover this, especially when we are told that the routes will not be combined, as clearly a lot of preliminary work has gone on here to make it possible. Otherwise... why bother? So presumably all the other service prefixes must mean something. Has anyone worked out a list?
In reality, each service has a 4 character code, known as a headcode or train reporting number - they're shown on the Working Timetable which shows all services that run in reality, and are mainly used by signallers to identify each service. Presumably this was used to create the in-game timetable on both routes. Whoever built the timetable has simply put that code in the name of the service in game. Have a look at this for more general information: https://en.wikipedia.org/wiki/Train_reporting_number (note this doesn't apply to London Underground); or here for info specifically for BML: https://forums.dovetailgames.com/threads/london-to-brighton-headcodes.50264/
By whom? To the contrary, Matt has said that route merging is something DTG hope to be able to do, eventually, and that keeping that potential open is a factor that goes into route and timetable design. (As for the service alignment between BML and ECW: BML's timetable is the real life one, more or less; and I don't know if that's true of ECW but it has the feel of being legitimate, so it's unsurprising that they would have the halves of the same services)
I think you are being a bit too optimistic here. DTG is not completely shutting the door on combining routes by using real world coordinates in the maps and keeping the service numbers consistent, but at the same time they recognize that there are huge technical difficulties that would need to be resolved before they could do route merges the way they would want to do it. Of course they explicitly said they are not actively working on this. If you ask me, I think our chances of seeing this implemented into TSW2 are very slim. Hopefully for TSW3 or whatever comes next in a few years.
