Question: What date was Sonam Sherpa's band officially formed?

Context paragraphs:
Mandrake Project: Mandrake Project was a band officially formed in 2002 and based in Pittsburgh, PA.  (Not to be confused with another UK-based band of the same name) They are known for creating predominately instrumental music that defies solid genre categorization.  The tag "cinematic" stemmed from listeners' and critics' references to how the music fits to visual stimuli and thematic imagery from films.  The band has also been referred to as crossover progressive, ambient, jam-band and even jazz-rock.  Mandrake Project's eclectic music is accented by its shared membership with groups like The Polyphonic Spree, The Twilight Singers, and New Invisible Joy and The Afghan Whigs.

Pontiak: Pontiak is an American neo-psychedelic rock band of three brothers from the Blue Ridge Mountain area of Virginia: Jennings Carney (bass, organ, vocals—born 1978, Washington DC), Van Carney (lead vocals, guitar—born 1980, Washington DC) and Lain Carney (drums, vocals—born 1982, Washington DC).  The band officially formed in January 2004.

Colour Coding: Colour Coding was an Australian indie pop band officially formed in 2011 and based in Sydney.  The band was formed by Chris Holland and Tim Commandeur, both members of the group Operator Please; after Operator Please's second album, cousins Holland and Commandeur began writing as Colour Coding.  The band released its first EP "Proof" in March 2012 with the lead single "Perfect" uploaded as a free track online in November 2011.

Sonam Sherpa: Sonam Sherpa(Hindi: सोनम शेरपा) is lead guitarist of Indian band Parikrama.

The Iron Heart: The Iron Heart is an American three-piece band based in Napa, California.  The band officially formed in 2013; however, the members had played in various projects with each other dating back to 2000.

Akalpith: Akalpith is a Marathi movie to be released on February 28, 2014.  The genre of movie is a 'psychological thriller' and is written and directed by Mr. Prasad Acharekar.  Movie starts with Renuka Shahane, Mohan Agashe and Nirmiti Sawant.  The theme song of movie is written by Guru Thakur and is composed by Sonam Sherpa, Nitin Malik and Subir Malik of Parikrama Band.

Full Blown Rose: Full Blown Rose (often abbreviated to FBR by both fans and the band) was an alternative rock band which began in New York City in 2001 and were produced by We3Kings Music (Seven and the Sun, Whiskey Falls and Have2Have).  Members included Josephine Conigliaro (lead vocals), Matthieu LeChevalier (drums), and Josh Allen (lead guitar).  The band officially formed in 2001 and officially ended in 2005 via their official website.  They received their widest exposure after their song "Somebody Help Me" was chosen as the official theme song to the Fox Network's short-lived supernatural drama Tru Calling.  Although they were never successful, Full Blown Rose subsequently developed a devoted fan base over the internet.

Parikrama (band): Parikrama (Hindi: परिक्रमा) is a rock and roll band from Delhi, India.  They have several live performances and original numbers to their name.  The band was officially formed on 17 June 1991 in Delhi.  The word "parikrama" means 'orbital revolutions' in Sanskrit.

Juicy Lucy (band): Juicy Lucy is a British blues rock band officially formed on 1 October 1969.  After the demise of The Misunderstood, Juicy Lucy was formed by steel guitarist Glenn Ross Campbell, and prolific Blackburn saxophonist Chris Mercer.  The group later recruited guitarist Neil Hubbard, bassist Keith Ellis, and drummer Pete Dobson.

Prithibi: Prithibi (Bengali: পৃথিবী) is a Bengali rock band officially formed in Kolkata, India in the year 2005.  But its original formation goes back to 2001 at Ashutosh College.  Presently the band consists of Kaushik (lead vocals, composer, lyricist), Ronny (guitars), Prosanto (bass, backing vocals), Raja (guitar, backing vocals) and Arnab (drums, percussions).  The band became more popular with audiences when they stood first runner up in a competition, Band-E-Mataram held in Kolkata by a music channel, Sangeet Bangla, record label Asha Audio and Sangbad Pratidin in 2005.

Supporting paragraphs: Sonam Sherpa Parikrama (band)
Answer: 17 June 1991