As the rock era has moved into old age, a phenomenon has emerged known as the “copyright dump,” where, due to a still vaguely defined European Union law, artists must release recordings before those recordings become 50 years old, or lose the rights to them.

This places the artists in the awkward position of having to choose between officially releasing sub-par studio recordings or concerts as part of their official discography or abandoning them to public domain, where anyone could release and profit from them without paying the creators. Thus, over the past decade or so we’ve seen artists from the Beatles and the Rolling Stones to Bob Dylan and Motown Records quietly and/or briefly release such recordings to renew the copyright, often just days or weeks before the end of that 50 th year. Dylan has released several “Copyright Collections” boxed sets in Europe in ludicrously small numbers; the Stones released nearly 75 mouth-watering late’60s live and studio tracks on YouTube for about 24 hours at the end of 2019; the Beatles’ iTunes-only “Bootleg Recordings 1963” collects 59 songs, mostly radio sessions or studio outtakes, that weren’t deemed good enough for their official multi-disc compilations.

Last year, Pink Floyd dropped a dozen early concerts onto streaming services for a few weeks — and more interestingly did the same last week with some 18 concerts from 1972, when the group was playing its epochal “Dark Side of the Moon” album in its entirety as much as a year before it came out (as first reported by Rolling Stone). The concerts, many of which seem to be repossessed bootlegs — vinyl scratches can be heard on a few — vary wildly in sound and musical quality and some are incomplete, but they present a fascinating timeline of the band workshopping an epochal album that quickly became one of the top-selling and most critically praised of the rock era.

The process of working out new material onstage before recording it was common for the time (although increasingly rare as CD bootlegs and then cellphones became ubiquitous) and Floyd did it for most of their peak years. A strategic needle-drop on these concerts, many of which are between two and three hours long, show the group refining the already-complete songs from “Dark Side” onstage: The versions on the earlier shows (best quality: Tokyo, March 3) are looser and less defined than the familiar ones, with a fair amount of improvisation and more-tentative vocals, particularly from Waters on “Money,” which also has some percussion flourishes that were soon abandoned. They gain confidence as the year progresses — Pink Floyd toured like crazy in these days, as these concerts document two separate U.K., U.S. and European tours as well as a Japanese one — and by the end of the year the performances on the album’s songs find the band at the peak of its instrumental powers. However, as is often the case with live Pink Floyd, they’re much weaker in the vocal department — many segments that are sung dismally off-key, particularly by David Gilmour, which places their often-sophomoric, first-rhyme-we-can-think-of lyrics in unflattering relief (and let’s face it, Pink Floyd’s lyrics have much less gravitas when you’re no longer a stoned teenager).

Just as interesting for fans are the performances of the band’s psychedelic-era songs, many of which got a final airing on this tour: Epics like “Set the Controls for the Heart of the Sun,” “One of These Days,” “Careful With That Axe, Eugene” and of course “Echoes” (which was performed as an encore later in the decade in a “Dark Side”-style arrangement with sax and backing singers) were played at most of the gigs, but occasionally the group threw in “A Saucerful of Secrets,” “Childhood’s End,” “Atom Heart Mother” and even an instrumental titled “Blues” that is exactly what it says it is.

There’s also a five-song EP including alternate versions of songs from the album, three of which are genuine outtakes (including an “Us and Them” without the echo on the vocal) while the other two are unofficial “Trance Remixes” that, as their title makes obvious, date from the early ‘90s and were rumored to be the work of dance-music pioneers the Orb but are now said to have emanated from an Italian DJ taking advantage of that country’s sketchy copyright laws of the era (many pristine-sounding bootleg CDs emanated from Italy in the 1990s). On a related note, although these recordings are credited to Sony Music’s Legacy catalog division, sources say that doesn’t mean the group, which has been shopping the rights to its masters for a price said to be nearly half a billion dollars, has sold them; the group continues to own its masters and the arrangement falls under Pink Floyd’s ongoing distribution deal with Sony.

The concerts are a bit tricky to find on streaming services and probably will not be available for long; last year’s batch were removed after a few weeks but can still be found on YouTube. On Spotify, look under “albums,” then “compilations,” click “show all” and scroll way down (assuming you don’t feel like searching for titles like “Pink Floyd Live at the Palais des Sports de L’Ile de la Jatte, Saint Ouen, France, 01 Dec 1972”).

Although this realm is most definitely not a place for casual fans, it’s fascinating to hear “Dark Side of the Moon” played in its entirely for totally unfamiliar audiences before it became Dark Side of the Fucking Moon, and imagining being among the first people on earth to have their minds blown by it.