Hereford to Bicester Town isn't valid via Banbury.
I don't think it's quite as simple as that.
Hereford is a Routeing Point. The four Routeing Points for Bicester Town are Banbury Group, Greenford Underground, London Group and Oxford. So we need to do a Fares Check to find out which Routeing Point(s) are appropriate for a Hereford to Bicester Town journey.
The Fares Check is Defined in "How to use the National Routeing Guide":
if you are not certain that a particular routeing point for the destination station is the correct one. Compare the fare from that routeing point to the origin station with the fare for the throughout journey - it is an appropriate routeing point only if that fare is the same or lower than the fare for the throughout journey from the origin station to the destination station. Note 1
For all fare types, Greenford and London have higher fares to Hereford than the Hereford - Bicester Town fare. So these are not appropriate Routeing Points for this journey.
For all fare types, Oxford has the same fare to Hereford as the Hereford - Bicester Town fare. So Oxford is an appropriate Routeing Point for this journey.
Banbury is a more interesting case. If travelling on a First Anytime ticket, the Banbury - Hereford fare (FOR = £69.60, FOS = £34.80) is higher than the Hereford - Bicester Town fare (FOR = £64, FDS = £32), so Banbury is not an appropriate Routeing Point.
But if travelling on a Standard Anytime Return (SOR) or a Standard Off Peak Return (SVR), the Banbury - Hereford fare (SOR=£36.30, SVR=£28.50) is lower than the Hereford - Bicester Town fare (SOR=£37.60, SVR=£29), so Banbury is an appropriate Routeing Point.
But there are five fare types between Hereford and Bicester Town where there is no corresponding fare from Banbury to use for comparison:
£42.20 First Off Peak Day Return (FCR)
£24.00 Standard Anytime Day Return (SDR)
£18.80 Standard Anytime Day Single (SDS)
£17.50 Standard Off Peak Day Return (CDR)
£17.40 Standard Off Peak Day Single (CDS)
"How to use the National Routeing Guide" states:
All fares comparisons must be made using the same ticket type.
If the customer requires a Single then Single fares should be compared. If the customer requires a Saver then Saver fares should be compared. In exceptional circumstances, due to local fares policies, a direct comparison may not be possible. If this is the case and the origin station or destination station has a lower fare of the type selected than all its routeing points, the Standard Single (Day or Open) fares should be used for comparison purposes.
This does not deal explicitly with the situation where there is no fare of the same type, but it does seem to imply that if one gets stuck, one should compare standard singles.
The £25 Banbury - Hereford SOS is higher than the £18.80 Hereford - Bicester Town SDS, so I think Banbury is not an appropriate Routeing Point for these five fare types.
In summary, Hereford to Bicester Town is valid via Banbury with a SVR or SOR ticket, but in my opinion not with a FOR, FDS, FCR, SDR, SDS, CDR or CDS.
Fares Simplification?!
John
Note 1 I think there may well be an error in the NRG here, and that it may be intended that one should compare the fare from the origin station to the routeing point with the fare for the throughout journey. It seems daft to compare a Hereford to Bicester fare with an Oxford to Hereford one. Fortunately, in this case the fares are the same in each direction but that is often not the case. Do others think that the NRG is in error here?
