Kits, Im on a bit of a learning curve here and following the Wiki https://wiki.openstreetmap.org/wiki/Buses as best I can.  It seems to imply the stop position node is not necessary .... apart from rare cases. Perhaps this is one of those ?
With regard to the Master Relation, does that not only come into effect once you have 2 or more relations in a route ?  With T4, I believe I yet have to add the return.
Appreciate the comment and feel free to add the Merthyr station so I can follow by example.  I would also strongly ask you to organise an amendment to the Wiki if stop position nodes should be used, and where its mandatory.
Rgds, Russ.