Clue #4: Subtly-Differing Teeth
Here's a look at Paul's teeth, but first it's important to note that he always shows the same basic pattern, having a recessed upper right eye tooth, and a protruding upper right incisor.
However, even while always maintaining this pattern, sometimes he shows upper left molars that arch outwards, and other times that point inwards.
Ed Sullivan 1964 and 1965.
During the song segment of The Night Before, his teeth are angled inwards for the first half of the number, then they are arched outwards for the second half.
This carries over after Beatlemania to the present day.