Dear Gil,

When you passed away in 2012 at the age of 75, you were eulogized by Rolling Stone magazine as the legendary A&M record executive who introduced the world to acts like The Police, Soundgarden, and Janet Jackson. You were remembered as the man who started A&M's movie division in the early 80s and produced the beloved film The Breakfast Club. You were one of the founding partners of ESPN's Classic Sports channel. You were known and remembered by titans in the music industry, including Sting, Herb Alpert, and Joe Cocker.

And yet most people have never heard of you.

The same can be said of the women featured in your final produced film, which shines a spotlight on the (ironically) unsung heroes of the music industry: session vocalists, or as they are more universally known, backup singers. When you hear the voices of Darlene Love, Merry Clayton, Lisa Fischer, Tata Vega and others, you can't help but wonder why they aren't massive stars. Bruce Springsteen, Stevie Wonder, and Mick Jagger are just a few of the rock gods interviewed in the doc, and they seem just as confused as I was by the lack of notoriety given to these incredible singers. Indeed, it's impossible not to have respect for the women responsible for some of the catchiest vocal hooks in pop music history. Like you, Gil, these women seem to be renowned only by industry insiders. I wonder: was it this kinship that drew you to the project?

It takes a certain type of ego to give up the relative safety of toiling in anonymity to pursue super-stardom. Many singers interviewed maintain that singing backup is far less stressful and therefore more rewarding. Yet nearly every one of them has released a solo album to little or no fanfare. Lisa Fischer won a Grammy in 1991 for an R&B hit…and never charted again. We see her standing in line at the post office amongst people who have no idea that she has sung backup on every Stones tour since 1989. Darlene Love - probably the best known of the unknowns (an honour akin to being valedictorian of summer school) - is widely regarded for being the prototype for every backup singer that followed. She signed a devil's contract with Phil Spector that kept her under his thumb, and by the mid-70s she was cleaning houses to pay her bills. It's criminal that she might be best known for playing Danny Glover's wife in the Lethal Weapon franchise. Merry Clayton, another unsung backup, recalls that she was pregnant and in curlers when she got a call to come down to the studio at two in the morning to belt out the iconic line "Rape, murder/It's just a shot away" in the chorus of "Gimme Shelter." No one owes her pipes a debt of gratitude more than Martin Scorsese.

20 Feet has fingers in a lot of narrative pies, but it's most interesting when it focuses on the singers' struggles in a historical context. Most are black daughters of preachers, which would explain the call-and-response nature of their early gigs with legends like Ray Charles and Ike & Tina Turner. As the British rockers who built their sound around American blues gained popularity in the 70s, they turned to these same black female singers to give their records the Delta soul sound they craved. More than one performer noted that it was this cultural appropriation that gave them the most freedom as vocalists. This era would be the apex for most backup careers.

You were known as a nurturer of singers and songwriters at A&M. You allowed artists to mature. If only you had lived long enough to do the same with 20 Feet From Stardom. Instead of focusing on two of the more resonant storylines - those of Darlene and Lisa - the film overextends itself by laying down too many over-produced backing vocals. Had you lived to guide this project to fruition, it might have finally put you on the map.

20 Feet From Stardom aims for the heart, hoping, it seems, to duplicate the success of last year's Oscar winner Searching For Sugarman, another doc that profiles a singer who shoulda- coulda-woulda been a huge star. Unfortunately, the aim is off here. Where Searching takes the audience on a magical mystery tour, 20 Feet languishes behind the music. Sure, it has a great beat, and you can dance to it, but it's more of a one-hit wonder than a timeless classic.