If you grew up in the ’60s – if you were, so to speak, a Fabs OG – you probably counted out your adolescence in Beatles 45s, the precise order of which are as engraved in your memory as the birth order of your own children.

If you were a teenager in the ’70s, you probably know the band through the prism of mum and dad’s copies of the Red and Blue double albums, which stood sentinel alongside so many music centres with their smoked-glass lids.

For the Smash Hits generation of the ’80s, the death of John Lennon brought the realisation that the Double Fantasy chap had once been in a group with the leader of Wings and the further realisation that this group sometimes sounded a bit like ELO.

When Britpop arrived in the ’90s, it came not so much to bury the Fabs’ legacy as to raise it to new heights. Around the same time, the remaining “Threatles” told their story in their own way via the TV mini-series Anthology and its accompanying DVDs and compilation albums.

At the turn of the millennium, at the cresting of the CD boom, they released 1, another compilation album, which has sold more than 31 million copies and remains the only CD that most people under the age of 25 can remember.

Six years after that, original Beatles producer Sir George Martin and his son Giles were tasked with producing a “mash-up” of old Beatles recordings for a Las Vegas show called Love, to be performed by Cirque du Soleil.

Giles Martin recalls thinking it wasn’t all that good an idea, so he decided to make sure his work wasn’t wasted by backing up all the original Beatles tapes and making musical notes about each of the original recordings.

Almost 17 years later, Love is still running in Las Vegas with no end in sight, the business of the Beatles is still being run from a smart townhouse in Knightsbridge and Giles Martin is still working on new releases bearing the Beatles name.

The most recent is Now and Then. This was one of the John Lennon demos that Yoko Ono handed over in 1994 when Anthology was being made. The others were Free as a Bird and Real Love.

At the time, the technology wasn’t up to the task of separating Lennon’s voice from his piano accompaniment, so Now and Then was abandoned and, says McCartney, “left to languish in a cupboard”.

There it would have remained, had it not been for McCartney’s work ethic. Having been impressed by how director Peter Jackson had managed to isolate all the individual voices from the mono tape recordings that went into his epic Beatles documentary series Get Back, he wondered if Jackson’s machine assisted learning technology might do the same with this dusty cassette.

It turned out that it could. “There it was, John’s voice, crystal clear,” says McCartney in a short film made to mark the release. “It’s quite emotional.” Hence the record they’re calling “the last Beatles song”.

It’s always Paul. Ringo often reflects that the Beatles only made the number of records they did because Paul was always on the phone. It’s little different 60 years later.

Ringo says: “He called me up and said he’d like to work on Now and Then, what do you think? I think it’s great. So he put the bass on, he sent the files to me, I put the drums on. It was the closest we’ll ever come to having him back in the room, so it was very emotional for all of us. It was like John was there, you know. It’s far out.”

All statements from Planet Beatle are careful to reflect the views of all four principals. George Harrison’s widow Olivia says she has no doubt that her husband would have wholeheartedly supported the project, while John Lennon’s son Sean said “it’s like a time capsule and all feels very meant to be”.

But still the key Beatles fan is Paul. “We all play on it, it’s a genuine Beatles recording. In 2023 to still be working on Beatles music, and about to release a new song the public haven’t heard, I think it’s an exciting thing. How lucky was I to have those men in my life and to work with those men so intimately and to come up with such a body of music.”

The final piece of the puzzle is a video for Now and Then, directed by Peter Jackson; his first pop promo is an unashamed piece of fan fiction, in the timeless new dimension of hyper-reality.

Giles Martin remains more concerned with the sound than the pictures. “I thought it was really important that it sounds like the Beatles, and the Beatles would have put some backing vocals on it. But they’re not there any more. So, I went through my notes. An ‘oooh’ is an ‘oooh’, and there are lots on Because and Here, There and Everywhere, so we used some of them.”

The 21 tracks that have been added to the 50th anniversary reissue of the Red and Blue albums were chosen with a view to redressing a previous imbalance between Lennon/McCartney and George Harrison songs.

The inclusion of the likes of Tomorrow Never Knows, Lucy in the Sky with Diamonds, Dear Prudence and I Want You (She’s So Heavy) reflects the trippier music favoured by today’s Beatles streamers.

“The Red and Blue albums were the first Beatles albums I really knew,” says Martin, who was born in 1969, the year his father produced Abbey Road and the Beatles began to wind up. “I went on a ski trip when I was about 10, and a mate of mine had the cassettes, so we pretended to be ill and listened to those.”

On these, the first reissues in what was then a novel technology called “stereo”, the sound of the band was all in the left channel with the vocals over in the right. This neither did justice to the bracing whomp of the original mono singles nor matched the deep-pile sound of other 1973 releases like Pink Floyd’s The Dark Side of the Moon.

Martin is pleased that today’s technology doesn’t merely allow the drums to be extracted from the original tape. “You can also de-mix the de-mix so that you have the different parts of the drum kit on separate tracks,” he explains.

“On Nowhere Man you can have the harmonies in stereo. I end up replaying Ringo’s drums through a speaker on the floor of Studio Two at Abbey Road, then re-recording them. That’s very eerie, if you go in the control room and the Beatles are playing downstairs.”

No matter what the song says, there’s no getting back. In the ’60s, all pop music sounded best at a fairground, where you could feel the bass. In the ’70s, Abbey Road became everyone’s favourite Beatles album because you could play it alongside Fleetwood Mac. In the ’80s, people listening to Beatles CDs were thrilled by the absence of scratches. From the ’90s, most music was accessed on headphones.

At each stage, we have listened in a different way while kidding ourselves it’s the same.

Read more:

• The Beatles’ last ever song confirms November release date
• BBC Two and iPlayer announce The Beatles celebration night

In 2011, Giles Martin was hired to mix the sound for Martin Scorsese’s documentary George Harrison: Living in the Material World.

“I was fired because they said, ‘Marty doesn’t like your revisionist approach to music.’ Four weeks later, I was called back. I met Marty in a studio, we set up the film and I switched between my mix and the original.

“He said he preferred my mix and he couldn’t understand why. I said it’s because it’s never how you remember it being. Our brains adjust. We don’t really listen to these things. We recreate them in our heads. My job is to mix a song so that it’s how people remember it.”

The real target audience, who are people like Giles Martin’s teenage daughter, have no such memories to contend with. “I drive teenage girls around and I say, ‘What’s your favourite band?’ and they say, ‘They’re called Fleetwood Mac – I don’t know if you’ve heard of them’.

“My daughter recently went on holiday with [actor] Dominic West‘s family, who are all massive Beatles fans. They were listening to Here, There and Everywhere. She was able to come back and say, ‘Dad, I actually like the Beatles!’”

Seems like Derek Taylor was right.