Once again, if the Gateline is set appropriately, none of the above is required.
I gave a random example earlier - lets try a specific one... Lets be specific.
Between 1745 and 1815 on platforms 1-6 at Paddington ^ all of which are either unbarriered or controlled by the same gates^you have the following scheduled departures.
Platform 5 1745 Swansea
Platform 1 1748 Cheltenham
Platform 2 1800 Bristol
Platform 4 1803 Golden Hind
Platform 3 1815 Swansea
Only one of them does not set down at Reading. How can you properly control the barriers / gateline to stop reading passengers accessing the platform for the 1803? The only way would be to put a person on every door to the train and stop anyone with a reading or oxford ticket from boarding the train at Paddington.
You couldn^t really implement it at Reading either unless you stopped people at the exit door of the train. Lets say I was on the 1800, got off at Reading, stopped to spend a penny either figuratively or literally in one of the upper crust sorts^.then tried to depart the station just as the 1803 was letting out its passengers?
The ONLY way to stop it is a human ticket check on the doors of the 1803.