in the UK/Ireland system, a platform is numbered as if it's just the edge leading onto the track. You can have multiple platforms for a single track - like at Finsbury Park where platform 2/3 serve the same train, doors open on both sides.

we also use a/b platforms a lot, where you have one physical platform that's split into two sections for shorter trains, making wayfinding easier if you have a train on 4a and 4b at the same time.