Thanks for the input, everyone. For the avoidance of doubt, this is the ticket I have, and I am making the return journey this evening:
https://www.brfares.com/!faredetail?orig=TOD&dest=BTH&rte=700&tkt=SOR
Provided your ticket is routed "not via London" rather than "via Stafford", then yes - map combination AW+CU permits it if you go via Accrington. Bizarrely it's not permitted to go via Newport if you get to Manchester via Rochdale (the obvious route).
In practice I don't think anyone would bat an eyelid since the ticket is valid for use via Rochdale if you continue via Birmingham, and the Northern guard/barrier staff aren't going to know that you're planning on taking TfW rather than XC.
It's clearly an oversight as travelling via Newport is a perfectly reasonable route.
As it happens, the trains that I'm planning to catch requires a change at Crewe, where both valid routes intersect, which I guess makes this a particularly low risk.
By the way, when you say via Accrington, I'm assuming that means changing at Preston (and Blackburn, Accrington or Burnley). In which case, am I right in assuming doubling back at Preston is valid? (I might decide to go that way anyway, if there are disruptions.)
Thanks very much