Waheguru ji ka khalsa waheguru ji ki fateh.

it is an accepted fact that the "GRANTH" scribed by bhai gurdass ji in the presence of GURU ARJUN ji, was incomplete...as the Gurbani of Guru teg bahadur Ji had yet to come in 1604. During the time of Guru Hargobind Ji to Guru Gobind Singh Ji many hundreds of copies of this granth may have been made and as the enemies of the Panth were in "chardikala" at this time, many extras would have been added in...Bhai banno Bir is an example of addidtions made during Guru Arjun Ji's life time itself...so what about after his Shahedee and all his maal asbaab including the granth being given to Prithi Chand by Jehangir.
These unauthorised additions and the need to include Guru Teg bahdur Ji's GURBANI must have necessitated the Rescibing of the GRANTH JI by Bhai mani Singh in the presence of Guru Gobind Singh ji.
Sikhs beleive that ALL the ten Gurus were ONE JYOT - Nanak and proved it by using only the nanak name in writing all Gurbani. Since Guru Gobind Singh ji never used the name nanak in his Bani, he decided to NOT include His banis in the Granth Ji. As such GURU GOBIND SINGH JI decided to end all HUMAN GURUSHIPS and bestow Gurgadhi on Guru Granth ji..the rewritten AAd Granth of Guru arjun ji.

It is totally un-necessary to question why Guru arjun didnt call this granth GURU or why Guru Gobind Singh ji did any additions.... ALL the GURUS are ONE JYOT and not separate...and each had his part in the overall Master Plan unveiled by GURU NANAK... so its pointless to argue why this and why that. IT was GURU GOBIND SINGH JI's mission to proclaim GURU GRANTH as GURU in 1708 and He had every RIGHT as He is GURU NANAK the Tenth....and as the Tenth Nanak jyot Guru Gobind Singh had every right to alter/add/ to the "aad Granth ji as He saw fit. It is not as if an ordinary sikh is doing the adding/altering of gurbani. As the Tenth nanak Guru Gobind Singh ji knew what was GURBANI and what is extra. Guru gobind Singh ji left the Mundawni Mh 5 and Final THANKSGIVING Slok Mh 5 put in place by guru arjun as in the original Granth Ji....any subsequent "additions" by unauthorised peoples during the 18th century of turmoil could only be put in AFTER the Final Slok and thats why the raagmala appears in that position. Due to the Unique numbering/totals/and poetic composition of gurbani as well as other controls put in place by guru Arjun ji, and the unique Grammar of Gurbani...no one could add or alter any Gurbani....thats why we cna safely say Guru granth ji has come down to us as Guru Gobind Singh ji wrote it.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/history-of-sikhism/200-harimandir-sahib.html
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=200

Jarnail Singh