Detailed information on short platforms is now available in the Sydney Trains GTFS bundle and Trip Planner APIs.
The data is in GTFS-vehicles specification, which can be combined with set type and car elements in Sydney Trains trip_IDs. Consumers will now be able to convey which cars passengers will be able to alight from for any given trip. Detailed documentation is available here.
Note that trip_IDs in the NSW Trains GTFS bundle have also been updated to convey set type and number of cars scheduled for diesel and regional services.
The Trip Planner API documentation is also updated here.
Please note that TfNSW owned PIDS, website, and applications are only advising which cars to travel in where the trip is on an intercity line, and the destination platform is shorter than the train.
More information is available at https://transportnsw.info/travel-info/ways-to-get-around/train/travel-in-correct-car