The situation at the moment is that in the timetable database, there are no Sunday Liverpool to Manchester Airport via Chat Moss trains after Sunday 6 September, and there are no Saturday Liverpool to Manchester Victoria via Chat Moss trains after 24 October.
When I noticed this last year, I assumed it was for the Ordsall Chord works which, when these timetables were drafted in the second half of 2014, were expected to begin this year, for completion in 2016.
However, as has been pointed out, the published paper timetables all seem to show normal services, and Ordsall Chord has been delayed, so I would expect the paper timetables to be correct and the missing trains to appear in the database in due course.
We are well outside the 3 month window for these dates, so there is no reason for the timetablers to rush to update the database, as long as they do it by early July. I wonder if they'll be inserted as electric services? Probably not.