IRL the class 313/2 used to run to Eastbourne from Brighton, however in TSW i don't see any services to or from Eastbourne at all using the class 313, only services to Seaford & Lewes. Why is this?
Probably some artistic licence... When the route was built it was exclusively the Class 377 on passenger trains. The 313 was added as a after thought to the 2009 timetable. Atleast that's how it would seem?
The reason is because Southern only used the 313's for short services on the Coastway Routes like 1 hour or less due to the lack of restrooms and AC on the train. Most of the 377's don't terminate at Eastbourne they continue to Hastings or Ore. So that makes the run too long for the 313.
Yes the timetable in the game was based in 2019, 313's were removed from service in May of 2023 in real life.
the class 313/2 never served Eastbourne. The plan was to go that far but they never did. According to a friend who were very familiar with the southern territory around the ECW.
313s did serve Eastbourne until around 2017. An AM Brighton - Ore return working and a one-way PM run from Brighton to Eastbourne. These journeys are correctly shown in the mod timetable available for East Coastway.