But unless you know which trains you are going to have your ticket checked, you can't total a notional "fare paid". You either take a chance each time, and risk (rightly) being caught for faredodging, or you pay the full amount each time.
Maybe I'm missing something, but how are you working out which "fare" you would have paid had you had perfect foresight?
I observed over a month that there was NEVER a ticket check on return journey and never b4 Oxford on way down. Even when checked it was never by a train manager who had any idea where u might have got on.
I am not including non checks where the tm looks at me and basically says I can't be bothered - that is a check.
I would never do it but I pay 640 a month with discount and I reckon u could escape paying only 200 Osh in the current set up without much risk.
That's a he'll of an incenti e to chance it.