FPS submission having changed payroll software

SUGGESTED

I migrated to Sage Payroll from freeAgent this taxyear, so upto Month 8 I submitted to HMRC online via FreeAgent, and Month 9 onwards via Sage.

When i submit the FPS through Sage do i need to include all of the values upto Month 8 in the submission, or just the values paid via Sage?

I am already showing as owing too much tax having entered the YTD figures when i moved to Sage - a situation that is proving somewhat challenging to resolve as I can neither fix this through Sage, FreeAgent or the Basic PAYE Tools app - so i am worried about this 'double accounting' - or do HMRC only accept the FPS from the employee running the last payroll?