Analysing lyrics and album covers for hidden meaning and symbolic interpretation became popular in the 1960’s. Each ‘clue’ can be refuted with facts.
For instance, the black armband Billy/Paul is wearing on the Sergeant Pepper cover which supposedly said OPD, meaning Officially Pronounced Dead actually was an Ontario Provincial Police badge.
When John Lennon supposedly sang “I buried Paul" at the end of Strawberry Fields Forever, he actually says "cranberry sauce."
As for the number plate that declared that Paul would have been 28 if he had lived – Paul would only have been 27 at the time of the photo.