I seem to recall Star Wars was being heavily promoted prior to its release and had been released in the US in May of that year (UK was November 1977) but then there weren't actual UFOs in Star Wars. Close Encounters wasn't released in the US until November 1977.
I just feel there is a major clue to all this in that there is no shortage of sheep farming in Wales yet the UFO accounts seem to have focused on those farms that were keeping cattle. BSE (Mad Cow Disease) was first seen in UK cattle just seven years later and science still doesn't know the exact origin (
https://www.bbc.co.uk/programmes/m001rrhy) but rather the number of human deaths was thankfully small and so the public lost interest and slaughtering methods were changed.
In fact, writing this has reminded me of a personal connection with all this. In the late 1970s/early 80s my family were friends with a farming family near our home in north Devon. My sister and I used to go and stay on the farm at weekends and during the school holidays and I became good friends with their son (fun times driving tractors and exploring the farm). They had a milking herd and told me in all seriousness they had a UFO sighting from their car whilst on the farm drive (rather like Pauline Coombes). They also produced beef and had bought a bullock from market that turned out to be "mad" but this was in around 1984 before it was understood that meant BSE.
So, were these UFOs actually some sort of clandestine testing programme in response to insider fears about scrapie in sheep, the human form of CJD amongst cannibals and the feed producers grinding up cattle remains from as far away as India* to feed to cattle?
*Back then container loads of cattle remains were being shipped from places like India via the Netherlands until one consignment contained Anthrax and killed a dock worker (
https://www.bbc.co.uk/programmes/m001rrhy)