I have started a new thread to continue from GWR GF lock terminology (http://forum.signalbox.org/viewtopic.php?f=2&t=7846
) as it is becoming increasingly detached from the original theme.
I have now found the whole video of the September 1964 trip from Carmarthen to Aberystwyth from which the two clips in my post in the previous thread were taken. It is at https://vimeo.com/103641050
and it shows a complete journey over the line, including its branches. It is interesting in its own right, showing as it does full-sized staffs with Annett's key in use and some very ancient McKenzie & Holland signals, but in relation to the use of pilotmen it starts to get relevant at 18:30 at Strata Florida.
Up to that point everything has been entirely as you would expect with every appropriate signal being worked and the use of staffs/tokens much in evidence. You see the train run into Strata Florida station with the home signal in the clear position but it then leaves past the loop starter at danger. After that, every signal that is shown is in the on position until the train gets to Aberystwyth at which point normal working is resumed.
This northern section of the line closed (prematurely due to flood damage) in December 1964 but the rest of the line followed in February 1965 so in September 1964 the closure must have been a certainty. I wonder if some catastrophic signalling failure (destruction of the pole route in several places for instance) meant that it simply was not worth repairing things in view of the imminent demise and that extended pilotmen working was the chosen solution? However, as has been pointed out, that would not explain the complete absence of signalmen at any of the intermediate boxes, nor why some better method of working is not in use (Train Staff and Ticket for example if the timetable did not permit OES to be used). The length of line involved was not that great so a single Sunday's work could also have seen all the signal arms removed, particularly in the knowledge that they would never be put back. Altogether, very peculiar!