Hopefully someone will have the WTT's after 1965 / 66 covering Blackpool, if they do I hope they will spend a little time letting us know the train movements.
It would give us a better understanding of what happened.
In my experience, rail trips from various parts of the country to Blackpool for the illuminations tended to be one-off special excursions (Merrymaker or Pleasure-seeker ADEXs) rather than dated scheduled services....much like the coach trips really.
I agree. I'd imagine that rather than the WTTs, the really interesting stuff with any one-off specials or excursions would be shown in the Special / Weekly Traffic Notices from the period.
I've spent a bit of time in the past trawling the likes of eBay to collect Working Timetables for my own areas of interest. Not too hard to find the full WTT books (if you're willing to pay ££), occasionally you see the Supplements to the WTT - but I don't ever remember seeing any Special Traffic Notices up for sale.
Maybe these were printed on flimsy, cheap paper like the Supplements and, together with their ephemeral nature, very few have survived into the 21st century. And any interesting ones which did survive are tightly held by collectors of this kind of thing, or in society archives.
Regarding the run-down of Blackpool South,
this link shows an image of the diagram in the LMR-built box at Blackpool South just before abolition in 1982, when it worked double-track Track Circuit Block to St Anne's Station box and the terminus still had two operational platforms.
Often at signal boxes where infrastructure has been rationalised, the existing diagram was amended by simply pasting over all the removed track. In the case of this diagram at Blackpool South, there doesn't seem to be room either for the tracks towards the carriage sidings, which still extended to the Bloomfield Road bridge after 1964, or for Platforms 3 & 4 and the line from Marton, which was still in its last couple of years when the box was commissioned. The lever frame, on the other hand, has a good collection of white levers. Presumably the original (1965 vintage) box diagram was totally replaced sometime after 1970.
For the signalling situation on the Blackpool South "siding" after 1982, see
this link to Ingy the Wingy's Flickr pages - Kirkham box's diagram before its closure in 2017.
[EDIT] And
another link of the rare-as-hens'-teeth variety (from 70023venus2009's Flickr photostream) with a steam loco (identity disputed) in the Down Marton line platform at Blackpool South and dated 1966. So after the line was truncated at Blackpool South, but before final closure of the Marton Direct route. (Not to say that this loco had actually arrived along the Marton line - it may have been a shunting manoeuvre from the carriage sidings)