Before the band that would Change the World became The Beatles, the template for all rock quartets to follow, they had a floating lineup of many musicians of varying talents, generally taking the stage with six members.

In addition to guitars and drums, they had washboard, banjo and “tea-chest bass” players in their aggregation, that last instrument homemade with a wooden box, a stick and a string.

They played the jazzed-up folk/blues that was all the rage in the U.K. of the late 1950s, skiffle. And their name came from the corner of Liverpool where most of them grew up and the boys’ school many of them attended — Quarry Bank High School.

“Pre Fab!” is an amusing, informative and bittersweet documentary about the “forgotten” players in a band that would be founded by John Lennon, and would eventually include Paul McCartney and George Harrison, The Quarrymen.

If you’re a Beatles “completist,” you’re going to know at least some of this story. But this new documentary from the director of the equally fab “Women in Motion,” about the NASA career of “Star Trek’s'” Nichelle Nichols, rounds up the survivors of that group, including Paul McCartney, to talk in depth about those years. We get insights about the relationships, influences, group dynamics and key moments that took that teen group to the very pinnacle of fame and success when they formed and reformed as The Beatles.

You think you know The Beatles? You don’t unless you know Colin Hanton, Len Garry, Rod Davis, John Duff Lowe, original “manager” Nigel Walley and the other Quarrymen and their first-hand accounts of pop culture lightning st it struck just after their time getting to know John, Paul and George.

The anchor interviews are with Quarrymen drummer Colin Hanton, a twinkly retired upholsterer who makes “Life isn’t fair” a cute running gag as he recalls his near-miss shot at fame, and the co-writer of his memoir, Lennon curator Colin Hall.

They and Beatles historians, along with John Lennon’s half-sister, Julia Baird, Billy Bragg and musician, Beatles contemporary and Apple Records A & R guru Peter Asher paint a picture of post-war Britain, the generation that grew up free from fear of air raids and bridling at the country’s hidebound classism and genteel working class poverty.

And they flesh out the cast of characters in this “garage band without a garage,” filling in the blanks of how this fellow knew that one, who got who into the band, an ever-shifting lineup of teens who embraced Lonnie Donergan’s wildly popular, high-energy cover of “Rock Island Line,” sort of the Ur Text of Skiffle.

Some of them were ready to adapt as the band embraced Buddy Holly, Little Richard and American rock’n roll. And some were washboard, tea-chest bass and banjo players.

There’s terrific stuff like hearing the earliest surviving recordings and how they survived, band members relating how Lennon’s mother Julia knew how to play the banjo and passed on “banjo chords” and tuning to the nascent guitarists — like John — trying to get pleasing sounds out of their axes.

And there’s the also-ran players’ cheerfully-philosophical realization that McCartney, who knew proper tuning, and Harrison, already a very young guitar fanatic, changed the band and made it more likely they’d all drop-out or get pushed aside as ambition and professionalism set in.

Hanton is a spry, droll presence at the heart of these recollections, the film’s tour guide through the Liverpool of “Eleanor Rigby’s” grave, “Strawberry Fields” and tea-chest bassist Len Garry adds a cheeky sparkle to the testimonials.

The film’s history makes it a must-see for any Beatles fanatic. But the third act’s adorable surprises and redemptive yet comic touches lift the film above simple history and take it into the realm of re-examining “Life isn’t fair,” because sometimes it all works out in the end.

This bright, sunny amd brisk pre-history makes a fine companion to Peter Jackson’s laborious but thorough “Get Back,” which lays out — in great detail — how the “Fabs” from “Pre Fab!” reached the end of their “long and winding road.”

As origin stories go, it’s hard to beat the self-effacing personalities and musical myth-building of “Pre Fab!” It’s finishing its festival run now. Hopefully, some smart distributor and rodent-mascot “Get Back” promoting streaming service will give this delightful musical history lesson a proper home.

Rating: unrated

Cast: Colin Hanton, Paul McCartney, Peter Asher, Julia Baird, Colin Hall, Sylvia Hall, Billy Bragg, Len Garry, Bob Harris and Rod Davis, with John Lennon and George Harrison (archival footage).

Credits: Directed by Todd Thompson, scripted by Mark Bentley, Joe Millin and Todd Thompson, based on the memoir by Colin Hanton and Colin Hall. A Stars North release.

Running time: 1:33