With the greatest of respect - for this is an excellent bit of detective work - but, really,I think you are in danger of falling down your own rationalist rabbit hole here.
Here are the problems I have with your hypothesis:
* As you say, the release of the film `That'll Be The Day` was several weeks prior to the girl's* alleged encounter in May 1973. On top of that, there is most often a fairly substantial interim between the shooting of a film and its eventual release - often well over a year - so the film may well have been shot a year or year and a half (plus the several weeks) before the `encounter`. I do take your point that the event of a major filming in that quiet region would have been the cause of a lot of local chatter - but a year or more later and in a way that would interest a seven-year-old girl who would never have seen the film?
* You make a lot of the parallels between the `encounter` (which begins with the retrieval of a book from a river) and one scene in the film. However, in the film scene a schoolboy very deliberately hurls some books, a schoolbag and his cap into the river (and no attempt to retrieve them is made) - whereas in the `encounter` one book is retrieved from the river which had ended up there by accident. Yes, maybe in the filming someone had the job of retrieving the books from the river - but as this would have been well over a year before the alleged encounter and any connection is a real stretch. Throwing books into a river and dropping A book into a river are different acts - and even a seven year old would make the distinction. (This is not to mention the inconvenient fact that - as Otter has pointed out - the locatiion of the filming is not even the same as that of the alleged `encounter)`.
* The `Sandown clown ` connection.
It is worth noting that the witness did not, at any point refer to the entitiy as a `clown`. Indeed, the image she uses is that of a `ghost` - which is altogether a different type of image. The `clown` moniker only started to be employed in retrospect - indeed even the original BUFORA article from January-February 1978 does not make mention of the entity as being a `clown` either. Now itf there is one iconic image that a seven -year-old kid is guaranteed to know, it is that of The Clown and yet the witness did not make use of the word as a description in her witness account.
So to go from that and then to make a connection with a two-dimensional image of a clown's face that appeared on the set of a film released several weeks before is really pushing things. Clowns are a common feature of fairground art - but this was not even real fiargound art, but a mock-up desiigned to look like an artefact from the nineteen fifties! Also I repeat, aagain, Fay did not even make reference to any `clowns` in her original story.
Sorry mate.
* We talk of `witnesses` in the plural - but the boy is a shadowy figure at best. We have no name or age and his only role seems to be to `confirm` the encounter - whatever that means. I think we have to be honest and admit that there is really only one known witness - a seven year-ol-girl called Fay.
