I posted this earlier but it didn't appear because I am away from home in a hotel with an abysmal wifi connection!
I don't think it is necessary to revise the NRCOC wording to allow "fastest route" instead of "shortest route". Instead, the allowed routeing guide routes - or maps - ought to always permit the fastest route.
I think the problem with the present routeing guide is that it seeks to "get away" with far too few maps, whereas a greater number of maps, but more discernment of which map is truly appropriate to a particular journey, will produce the best outcome for the vast majority of customers.
As others have posted, generally speaking the ability for a ticket from A to Z to allow travel via A, B, C, Z and also A, B, D, M, N, Z is rather less important than providing for every reasonable route between A and Z being permitted.
As things stand, the status quo favours the rare few who understand the routeing guide, at the expense of the vast majority who do not.