OK they are on the same line and are served by the same train(s). The line itself has a far more frequent service. Any help?
And here's me thinking it would be too easy.....
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It looks as though I've made it too difficult/obscure/boring so I'll give the answer and retire gracefully.
The answer I was after was 'the Oxfordshire halts', being Finstock, Combe and Ascott-under-Wychwood, each having one train a day Mon-Fri to/from Oxford, and Shipton, which has an extra to Oxford, and several from (though one is currently a bus) plus a Saturday service as well.