THE critical era between Blue and Hejira provides fertile territory for the latest sweep of the Joni Mitchell archives, which covers the three transcendental albums she recorded between 1972 and 1975 – For The Roses, Court And Spark and The Hissing Of Summer Lawns. These saw her music move increasingly towards jazz, while her themes also began to change, from the experienced-based songs of For The Roses towards the more general character studies of Hissing…. It’s a journey that’s explored here through numerous outtakes and demos from the three albums but most neatly articulated in the two live concerts that feature on the set – which is available on 5CDs or 4LPs, with a book containing photographs and a conversation between Mitchell and Cameron Crowe.

The first takes place at Carnegie Hall in 1972, with Mitchell producing beautiful, unadorned readings of her back catalogue plus several songs that would soon appear on For The Roses. Later in the box, which unfurls chronologically, there’s a set from Los Angeles in March 1974, with the LA Express, Mitchell’s backing band for Court And Spark. The new setting allows her to reinterpret some of the same older material, most notably the radical, almost trippy take on “Woodstock”, but even more fascinating are the changes rendered to fresher material. At Carnegie Hall, she introduces “You Turn On Me I’m A Radio” as a new song and delivers a fine but self-conscious performances. It’s an important song for this set: Mitchell had just signed to David Geffen’s label, Asylum, and he asked her to write a hit. The track was conceived as a sly dig at Geffen but went to No 25 in the US, and in 1974 she rips confidently through a song that has earned its place in the set. Similarly, at Carnegie Hall she plays “For The Roses” for the first time, almost apologetically; in LA, she introduces it with a seven-minute monologue, enchanting the audience, first with words and then with song.

As with all great artists, there’s no “better” version, simply different ones. Take “Cold Blue Steel And Sweet Fire”, one of her greatest songs. At Carnegie Hall it’s still raw – recently written and unreleased, possibly even unrecorded – but swoops and soars like a kite in a hurricane, its simple constituent parts building into something profound. Two years later at the Dorothy Chandler Pavilion in LA, Tom Scott’s sax highlights her progression towards jazz, and the song is more mature, more settled, but still startling.

The Carnegie Hall show concludes with a mass singalong of “The Circle Game” with Graham Nash, Stephen Stills and Jackson Browne, while the audience joins in. It’s a beautiful moment and Mitchell’s Laurel Canyon contemporaries pop up throughout this set, which begins with demos recorded with Nash and David Crosby. Neil Young and the Stray Gators play on a fat, awkward version of “You Turn Me On I’m A Radio” and there are two wild runs-through “Raised On Robbery” recorded at a Nash session, one with Young and the Gators in blistering form.

Although Young comes close, none of these artists ever tries to overshadow Mitchell. The only time you’d even know they were there is during some demos with James Taylor, Mitchell’s then-partner. The couple playfully work their way through a medley of classic rock’n’roll songs – “Bony Moronie”, “Summertime Blues” and “You Never Can Tell”, intimate but faded, like an aural Polaroid. Their difficult relationship inspired several songs on For The Roses, which was written when Mitchell left LA for a rural life in Canada. She then fell in love with LA Express drummer John Guerin, the muse for several songs on Court And Spark, including “Help Me”, the hit single that helped make Court And Spark her most successful album.

That brings particular attention to the set’s gorgeous medley of early Court And Spark tracks, as Mitchell sits at the piano and strings together “Down To You”, “Court And Spark” and “Car On A Hill” over 12 mesmerising minutes. The box is filled with such moments – The Hissing Of Summer Lawns demos are particularly gorgeous, as they present songs such as “Edith And The Kingpin” and “Don’t Interrupt The Sorrow” when they’re at their rawest and most simple. As well as the various demos and alternative takes from the three LPs, there are early versions of “Dreamland” and “Jericho”, songs that Mitchell wouldn’t record until Don Juan’s Reckless Daughter, plus For The Roses out-takes “Sunshine Raga” and “Like Veils Said Lorraine”, and a wicked version of “Bonderia” recorded during Court And Spark sessions.

It’s an embarrassment of riches, an apt term given that Mitchell sometimes seems embarrassed by her talent, displaying a humility that you don’t always find in her male peers. There are several moments when she introduces a song – live or in session – with a disarming giggle. Yet all the time, she produces astonishing music – arrangements, melodies, vocals, on guitar or piano – while subtly, almost imperceptibly, escaping her old self and leaving behind a set of amazing songs like a series of perfect clues.