Paul was supposed to die, not John. In the original history, Paul’s death in 1966 catalyzed the surviving Beatles’ transformation into something completely unlike their History B replacements. The Beatles-A never achieved the mega-mondo-ultra-stardom of the Beatles-B, but then, they never broke up and John wasn’t killed in 1980, either.
The hints in the music and album art of the Beatles-B are psychic bleedthrough from the original timeline. As time moves forward from the disruption point in 1966, the bleedthrough becomes more pronounced: people find clues that weren’t there before in the music, the legend becomes widespread and refuses to die in the face of — from the perspective of History B — factual debunking.
If the disruption isn’t corrected, the divergence will eventually become so pronounced that the rival timelines can no longer share the same metaversal coordinates, ripping each other apart in the attempt to exist independently. The first step to correcting the problem is figuring out who traveled back to 1966 to save Paul in the first place and why.