Castleford is a member of Pontefract Routeing Point Group. Mytholmroyd has three associated Routeing Points, Accrington, Halifax Group and Manchester Group. OK so a Mytholmroyd to Castleford Anytime Single costs £6.40. An Accrington to Castleford Anytime Single costs £18.60, a Halifax to Castleford Anytime Single costs £5.60, and a Manchester (All Stations) to Castleford Anytime Single costs £23.50. Therefore, only Halifax Group is an appropriate Routeing Point. The only map rule for Halifax Group to Pontefract Group is DP, the relevant section of which is this:
That means you can go in the first instance via Bradford or Huddersfield, in the latter case then by Wakefield or Leeds, then in the latter case by Wakefield or direct; if via Bradford initially from Leeds via Huddersfield and Wakfield, just Wakefield, or direct. Ergo, there are six Permitted Routes (my numbering):
1 Mytholmroyd → Bradford → Leeds → Castleford
2 Mytholmroyd → Bradford → Leeds → Huddersfield → Wakefield → Castleford
3 Mytholmroyd → Bradford → Leeds → Wakefield → Castleford
4 Mytholmroyd → Huddersfield → Leeds → Wakefield → Castleford
5 Mytholmroyd → Huddersfield → Leeds → Castleford
6 Mytholmroyd → Huddersfield → Wakefield → Castleford
Your outbound route via Mirfield is route 6 and your return via Leeds is (presumably) 1.