In fact, ABBA’s unreleased music catalogue is almost as long as the list of their released music. It is perhaps unsurprising given how mechanically complex their music was, and how their “sound” was achieved by layering the songs, instrument by instrument, and voice by voice, in the studio. The performers themselves lived in the land before autotune - not that they needed it - but the songs themselves were engineered to perfection.

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Over the years some of those lost songs have surfaced. I Am the City, recorded in 1982 for an unproduced album, finally made it out on the 1993 compilation album More ABBA Gold, and Put On Your White Sombrero, intended for the 1980 album Super Trouper, was released with the 1994 boxed set Thank You for the Music. And Get On the Carousel, never released on an album, can be heard in ABBA: The Movie.

Others were either given new lyrics, or new titles, and repackaged. Monsieur, Monsieur became My Love, My Life. In the Arms of Rosalita became Chiquitita, turning “happy, as you can be / in the arms of Rosalita” into “try once more, like you did before / sing a new song Chiquitita.” And Happy Hawaii (which was released) and Memory Lane (which was not) were both later reworked into one of the ’s bigger hits, Why Did It Have to Be Me?

And while ABBA’s “sound” seems to have survived intact - if there is anything in the new material to criticise, it would be that it is acoustically connected more to the 1970s and 1980s than to the 2020s, no doubt intentionally so - it is also true to say that in four decades the sound of the band, and in particular its two female singers, has also changed.

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In their original iteration, one of the band’s most powerful weapons was the smooth blend of Lyngstad’s mezzo-soprano and Fältskog’s soprano voices. On the new recordings, however, Fältskog’s voice is richer and more mature, slightly lower in register (so much so that one British reviewer mixed up Lyngstad and Fältskog’s work when the singles were released) and both voices sound less at ease with English lyrics, a natural enough side effect of four decades spent away from touring the English-speaking world.

At the same time, there remains something definitively ABBA about the assembly of new material for Voyage. The symbiotic communion of melancholy and joy that seemed to underscore their very best work: Slipping Through My Fingers, Hasta Mañana, Fernando and The Winner Takes It All. And the irresistible rhythm that suffuses their most addictive music: Waterloo, Dancing Queen, Money Money Money and Mamma Mia.

The upside? The album will be followed by a virtual concert experience, using “ABBA-tar” avatars, first in London, and then to tour worldwide. The downside? After the album’s release, the band will disband again, this time for good. Worse than the uncertainty of four decades of silence, it is a musical denouement that cuts deep.

“This is it,” Andersson told The Guardian when the new album was released. “It’s got to be, you know. I never said myself that ABBA was never going to happen again, but I can tell you now: this is it.”