The problem with the timetables is that they don't show everything that ran. It was common place for additional relief services to run, some with almost identical timings week after week. They were in effect timetabled trains that didn't appear in the timetable, something that some of us grumbled about at the time. So for example in the summer of 1988 from the end of June, and at least until the end of August, on Saturdays from Liverpool;
0908 Liverpool - Yarmouth
0925 Liverpool - Nottingham
Neither of which were in the timetable. Both were loco hauled Mk1 and neither involved running round as far as I recall (except the Yarmouth was a reverse/loco change at Norwich). Both were via the Hope Valley to Sheffield. The Yarmouth was then via Worksop, Retford curve and ECML to Peterborough. The Nottingham was via Beighton to Chesterfield. The lack of reversals doesn't help the OP although the simplest route from Liverpool to Skegness would have been to change trains off the Nottingham for a dmu to Skegness which may well have reversed at Grantham.