Timeline.
Pre Dec 2008 Manchester to Bolton had 3tph (1*Buxton to Blackpool Nth, 1*Man Airport to Blackpool Nth, 1*Man Airport to Barrow (2 hourly)/ Windermere(4 per day portion worked with Barrow)/Glasgow(4 hourly)/Edinburgh(4 hourly).)
The Manchester to Bolton to Preston corridor had 4tph once the timetable changed in Dec 2008. (1*Manchester Vic to Blackpool Nth, 1*Hazel Grove to Preston, 1*Man Airport to Blackpool North , 1*Man Airport to (Glasgow/Edinburgh) a few services to Barrow and Windermere remained but generally portion worked with other services. Other services cut back to Preston, Lancaster or Oxenholme)
Chat Moss Electrification announced in June 2009.
Manchester Airport to Scotland/Barrow routed via Wigan NW in 2013 (all services by Dec timetable change except portion worked Barrow with Blackpool). Manchester to Bolton to Preston down to 3tph.
May 2018 timetable change. Back to 4 tph. (1*Man Airport to Glasgow/Edinburgh, 1*Man Airport to Blackpool North, 1*Macclesfield/Stoke to Blackpool North and 1*Man Vic to Preston)
In May 2018 Bolton to Manchester will lose 1tph on the Wigan corridor and gain 1tph on the Blackburn corridor. Despite the Scotland to Man Airport services returning Bolton to Manchester Airport will remain 2 hourly due to the loss of Southport to Man Airport services. Bolton to Man Airport will drop to hourly in the peaks.