........ so far as I am aware, direct services to Manchester, at least from Burnley, never ran via Todmorden but used the shorter route via Accrington, Haslingden & Bury. There is no precedent for a Blackburn to Manchester via Todmorden service, so far as I know.
This has not been an easy issue to resolve but....
The LMS Timetable dated July 3rd to September 24th (incl.) 1939 includes the following:
Mon-Fri 348pm Manchester Victoria to York: First stop was Rochdale (arr. 407pm) from where the main train departed at 410pm running to York (arr. 556pm) via Brighouse and Normanton with a next stop of Sowerby Bridge (arr. 436pm). A rear portion departed Rochdale at 416pm and called at Todmorden (arr. 431pm, dep 434pm), Towneley (449pm), Burnley (Manchester Road) (455pm) and Rose Grove (arr. 458pm). The note in the Calder Valley Timetable (Table 149) states "Passengers from Manchester (Vic) for the Todmorden and Burnley direction travel in the three rear vehicles" another columnar note clearly states "To Burnley". Reference to Table 187 shows the train onward from Todmorden but makes no reference to it being a train from south of Todmorden but states that the 434pm from Todmorden is a "Through Train to Blackpool (North)" and gives an arrival time there, after many stops, of 642pm.
The way I interpret this is that the rear portion of the 348pm York express was detached at Rochdale and worked to Burnley as through carriages as explicitly stated in Table 149. These then carried forward to Blackpool (North) but were not advertised beyond Burnley (Manchester Road or Rose Grove?) at Victoria. Of course it is just possible that there were carriages working Victoria to Burnley and others Todmorden to Blackpool North and that they were combined into one train for the common section. Given the station times (3 minutes at Todmorden and 4 minutes at Rose Grove) this seems unlikely, though not impossible, as a lot of reformation could be done in a short time in those days.
Of course the war broke out during that Timetable and the Emergency LMS Timetable of "September 1939 Until Further Notice" still shows a 434pm from Todmorden as far as Preston, but only a connection onto a train from Victoria via one of the more conventional routes (being non-stop to Preston it is probably routed via Atherton and Chorley) beyond. The 348pm York Express is no more and a connection off the 325pm Leeds train from Victoria (itself the 230pm from Liverpool (Exchange)) provided for the Manchester - Burnley traffic.
Having found the above I've not looked further. Various dates in the 1950s failed to yield trough trains. The real delight of having old timetables on a desert island would be having the time to really examine them!
I hope that the above is of interest and would welcome any further information or comments.