References:
1. Sant Gurbachan Singh - 'Pehla Parkash' Katha
2. Kavi Santokh Singh - Gurprtap Sooraj
3. Baba Hari Singh - Gurbani Arth Bhandar
4. Kahn Singh Nabha - Mahan Kosh
5. S.H.A.R.E - Sikhi to the Max
6. Alphabet Inc. - Google

The pure belongs to Vaheguru, the victory belongs to Vaheguru.
Going back to history in 1592, poets had started to use the name ‘Nanak’ within their own poetry and would claim that it was Gurbani when in fact, such creations were meaningless when considered in the light of Gurbani’s message. Hence, people could mislead Sikhs with their personal teachings and manipulate the real ones. This displays just how popular the name of ‘Nanak’ had become that people would use the name to legitimise their own works. However, Guru Arjan Dev Ji considered the potential doubts that could occur amongst Sikhs with so much unauthorised words being propagated under the Guru’s name. In order to keep the authenticity of Gurbani intact, they decided for a compilation to be made of the true revelations. Guru Ji gathered the congregation of Sikhs within their court and ordered all to bring any Gurbani that they may have at home attributed to Guru Nanak Dev Ji. Hukamname (Letters of authority) were also sent far and wide to the Sikh masses to bring forth any written accounts of Gurbani that Guru Nanak Dev Ji may have propagated on their travels outside Punjab. Pehra Mokha Ji (a Sikh who had learnt the Gurmukhi script directly from Guru Nanak Dev Ji and was the scribe for the original ‘Janam Sakhi’) was instructed to write such letters.
As a result, literature such as ‘Praan Sangli’ was brought from Sangla-deep (an island situated in the south of India, now known as Sri Lanka) by Bhai Prana. ‘Ratanmala’ was brough from Kabul (present day Afghanistan) and Bhai Banno brought 59 Shabads which he believed to be Gurbani. ‘Pentis Akhri’ that presents pure Vedantic theories was also offered. Much other literature was brought to Guru Arjan Dev Ji in this same way from Sikhs across the lands. However, all of the such verses were ruled out by Guru Ji as being ‘Kachi Baani’ (that is Gurbani that was falsely attributed towards Guru Ji). Guru Amardas Ji also warns a Sikh against connecting with such words in their revelation ‘Ramkali M:3 Anand’:
“Without the True Guru, other utterances are false. The utterances are false without the True Guru; other utterances are false. The speakers are false, and the listeners are false; those who recite and preach them are false. They may continually chant, 'Har, Har' with their tongues, but they do not know God through what they are saying. Those whose consciousness is lured by ‘Maya’; they are reciting mechanically. Says Nanak, without the True Guru, other utterances are false. ||24||”
Raag Raamkalee, Guru Amar Daas Ji, Sri Guru Granth Sahib Ji, Ang 917
In this case, only the authentic Bani (words) was included within the compilation in comparison to other creations which were not accepted.
Some Sikhs informed Guru Ji of Gurbani ‘Pothiya’ (Volumes) that were kept in Govindval Sahib (located in the Taran Taran district of the Majha region of Punjab, India) in the house of Mohan Ji who was the elder son of Guru Amar Das Ji and requested that these should also be brought forward. Upon hearing this, Bhai Gurdas Ji (the maternal uncle of Guru Ji) stood up and volunteered to go and collect these volumes diligently. Upon reaching the house, and continuously knocking the doors and shouting aloud, there was no answer. The whole night passed but Mohan Ji remained seated in his ‘Chaubara’ (which is a room consisting of doors on all four sides of it, that is built on the house’s highest floor) within the state of a continuous Samadhi. The word ‘Samadhi’ is a combination of 2 words and 2 meanings. ‘Sma’ in Farsi (Persian) means sky and ‘Dhi’ in Sanskrit means Budhi (intellect). So combined together, when the intellect of a person becomes motionless like the sky, that duration of time is called ‘Samadhi’. There are 2 types of ‘Samadhi’: Sa-Vikalap Samadhi and Nir-Vikalap Samadhi and to keep this video on topic, the 2 definitions do not require any further explanation here. Bhai Gurdas Ji returned to Amritsar Sahib unsuccessfully so Baba Budha Ji volunteered to go and try his best to bring the revelations back to Guru Ji. Upon arrival to the house, seeing that Mohan Ji was still unresponsive and still sitting in a deep meditative state, Babaji broke the door’s hinges and removed the doors. Upon entering, they started to shake Mohan Ji in to different positions to awaken him but witnessing this, Baba Mohri Ji (the younger brother of Mohan Ji) warned Baba Budha Ji from proceeding in such attempts in case Mohan Ji feels disrupted and utters cursed words in anger towards such a respected Sikh that was Baba Budha Ji. Thus, both Sikhs returned to Amritsar Sahib empty handed.
Guru Arjan Dev Ji then went themselves to collect the Gurbani of the previous Gurus knowing this to be their task.