For a baby boomer like me, 12 years old when the Beatles broke through in 1962 and a mere 19 when they called it a day in 1969, it’s curious to watch the love objects of my teenage years still being pored over by grownups more than 50 years later. Writers such as Daniel Rachel may be adults today but they’re nonetheless too young to have experienced the Beatles in real time. They know more about their story than I do because they’ve read a lot of the books. Not all of them of course. Nobody could do that.

The first half of Rachel’s book is spent anatomising the discontents that set in once their manager Brian Epstein died in 1967, feelings that the four of them seemingly had to explain in every single interview they did for the rest of their lives. For 60s kids like me, it was neither a shock nor a mystery. In those days there were no bands with 40 years on the clock and therefore we had no expectation that this lot would continue. As McCartney points out, when a band are on the rise all the members’ energies are consumed by the climb. Once they plateau there’s fighting in the captain’s tower.

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Nonetheless, as Rachel painstakingly shows in his account of how they worked in their post-touring years, they had an ability to operate under conditions of personal tension that would have buckled most bands. They bit their lips. When John Lennon said: “Yoko only wanted to be accepted as one of us,” nobody offered the obvious rejoinder. Sometimes they expressed themselves more forcibly. In one passage the author wonders whether John really could have thrown a brick the 75 metres (246ft) it would have taken to break the front window of Paul’s home in St John’s Wood. More often than not the Beatles wrapped their troubles in work. When John decided he wanted to record The Ballad of John and Yoko as the new Beatles single, Paul didn’t object. He played all the parts John couldn’t, which was most of them.

The counterfactual second half of the book looks at the album that could arguably have followed, had they acted upon their plan to divide up the songwriting chores equally. It proposes a double album made up of songs that appeared on their early solo records. That means it contains everything from John’s Jealous Guy and George’s My Sweet Lord to Paul’s Maybe I’m Amazed and even Ringo’s It Don’t Come Easy. It tells the story of every one of those songs and, this being the Beatles, and there being nothing about the group that is not interesting, every tale seems touched by serendipity. According to US musician Leon Russell, even George Harrison, the member most ambivalent about the Beatles’ specialness, had already made a tape of just such an album at the beginning of the 70s. Certainly there are lots of great records in this track listing. However, there isn’t one that wouldn’t have been better if it had been recorded by the Beatles.

We who were there know that in reality it wouldn’t have been all jam

The group’s story remains the best in pop because it has a trajectory we retain in our heads. Their catalogue is perfect because they didn’t hang around to sully it. Abba, who enjoy comparable affection, are one of the few acts about whom you can say the same. The reason the Beatles’ reputation stands head and shoulders above everybody else’s is precisely because they didn’t release the lost album.

The cover asks us to imagine what would have happened if they hadn’t split up at the end of the 60s. Rachel’s book makes excellent stimulus material for a night down the pub with middle-aged Beatles fans who can’t help wondering about this. We who were there know that in reality it wouldn’t have been all jam. For a start, they would have had to hand over all the royalties for the lost album because of the inclusion of My Sweet Lord, which was plagiarised from He’s So Fine.

More widely, can we honestly imagine the inevitable desperation moves, like their disco phase, for instance, or that year they entered Eurovision and lost? Are we capable of imagining how we’d be feeling right now about their appearance at this year’s coronation? Could we imagine, even for a moment, being tired of the Beatles the way we get tired of most things? I think not. That was the favour they did us all by stopping when they did.

• The Lost Album of the Beatles by Daniel Rachel is published by Octopus (£10.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply