Simple answers are as follows.
1.GURBANI..is DHUR KI BANI that ONLY the "GURU" can pass on to us. From the Beginning it is..GURU NANAK SAHIB JEE....Mahalla Pehla...then Mahalla DOOJA, TEEJA, CHAUTHA, PANJVAAN. Guru Arjan Sahib Jee . Here Guru Arjan Ji deemed it necessary to Put all the Gurbani ucared so far by the First Five GURU SAHIBAANS into a GRANTH, Edited, compiled, made adulteration free each word accounted for in such a way that not a single word has been added or taken away since the day its jild Binding was done. The Firts and last attempt to adulterate it was CAUGHT RED HANDED by Guru Arjun Ji who named the adulterated copy KHAREE BIR (Salty granth copied by bhai banno who added some spurious banis on his own). This AAD GRANTH is now known as Kartarpuri Bir and in the PERSONAL POSESSION OF the SODHI Family of Guru Ramdass Ji-Guru Gobind Singh ji )
2. There are NO Mehlla Chhevan, satvaan and athvaan _ Gurus Hargobind Ji, Har rai ji and Harkishan Ji DID NOT UCHAR ANY GURBANI while they were GURU.
3. Guru TEG Bahadur Ji sahib then wrote some more GURBANI under the Mehalla NAUVAAN .
4. Guru Gobind Singh ji decided that He would NOT be passing the Gurgadhee to nay LIVING SUCCESSOR.
5. Guru Gobind Singh ji then undertook the task of WRITING another New Copy of Guru Arjan Jis AAD GRANTH ( that was in Kartarpur in the posession fo the sodhis who were ANTI-GURU GHAR) and INCORPORATE the additinal GURBANI uchared by Guru Teg Bahadur Ji sahib. This NEW COPY of the AAD GRANTH was penned by Bhai mani Singh Ji at Damdama Sahib (Now Takhat ) and is thus called the DAMDAMI BIR or DASVAAN PATSHAH KA GRANTH to distinguish it form the previous aad granth (AGS) of Guru Arjan Ji sahib at Kartarpur (which is INCOMPLETE as it is MISSING the GURBANI of Guru teg bahadur Ji)
6. THIS DAMDAMI BIR/DASVAAN PATSHAH KA GRANTH was given the GURGADHEE in 1708 at nanded when Guru Gobind Singh ji decreed..Sabh Sikahn ko HUKM hai..GURU MANIYO GRANTH !! THen this Granth became GURU GRANTH SAHIB (SGGS)
7. IMPORTANT POINT OF NOTE: The SGGS ( The WORDS.. AUTHORISED and CERTIFIED TRUE COPY OF Damdami Bir" are PRINTED on Each and every copy of the SGGS parkash in any and all gurdwaras ) .
8 Since 1708 after the demise of Guru gobind Singh Ji we have the ONE and ONLY GURU..and its SGGS. AT any ONE TIME..ONLY ONE GURU has uchared GURBANI..becasue ONLY ONE GURU sat on the THRONE of Guru nanak ji Sahib. Example..At the time GURU Nanak ji was alive..there was Bhai lehna Ji...Bhai Amardass Ji also around....BUT Bhai Lehna Ji never wrote asingle slok of Gurbani..UNTIL and AFTER he became GURU ANGAD. Same goes for Bhai Amardass Ji...equal in age to Guru nanak ji sahib...BUT "GURBANI" by Mehalla TEEJA began to spring ofrth ONLY fater Bhai Amardass ji became GURU Amardass Ji. same goes for Bhai jetha Ji...who became GURU RAMDASS ji and ucahrred GURBANI. "Guru" Arjan ji was Born in the Gurus Household.and Guru Amardass Ji gave him the blessings..Guru ka pota..Bani ka BOHITHA...Guru's grandson...the SHIP OF GURBANI at a very young age when the boy arjun sat in the lap of his grandfatehr Guru Amardass Ji !! BUT GURUBANI only came out of the pen of Guru Arjun Ji when he was GURU..and not earlier.
8. Guru Hargobind Ji was GURU..so was Guru Har rai ji and Guru Harkishan Ji..neither of them wrote a single word of Gurbani..BUT they are NOT ANY LESS "GURU". THAT is precisely why we say in ardass...SGGS...DASSAN GURUAN DEE JYOT !! Because the SGGS is the SUCCESSOR to the Gurgadee of GURU NANAK-GURU GOBIND SINGH...and the Guru nanak JYOT is NOW RESIDENT in SGGS. SGGS is the One and ONLY GURU by virtue of GURGADEE bestowed by Guru gobind Singh ji in 1708...it naturally follows that the SGGS is DASAAN GURUAAN DEE JYOT. Its doesnt matter if any GURU wrote or didnt write any Gurbani..the TEN gurus are ONE JYOT and THAT JYOT is now in SGGS. PERIOD.
9. LOgically since ONLY a GURU can uchar GURBANI..and the SGGS is NOW GURU...it logically also follows that whatever is INSIDE the SGGS is GURBANI. NOTHING ELSE...no matter what explanations..arguments...SIKH HISTORY is proof that ONLY THE GURU UCHARS GURBANI. PERIOD.
10 Next...Since ONLY the GURU can Uchar GURBANI..it follows that ONLY the GURU can alter...remove...add GURBANI. Now since the SGGS is GURU..that question no longer arises. Thus the SGGS is a CLOSED matter..and Guru Ji Himlsef Placed the LOCK..the FINAL SEAL..MUNDAWNNI MEHALLA PANJVAAN. Please realsie that even though Guru Gobind Singh ji REWROTE the entire AAD GRANTH into the GURU GRANTH...Guru Gobind Singh ji placed back the Mundawnni SEAL in the END as Guru Arjan Ji placed it. Its like a Caretaker opening a LOCK on a warehouse...placing additional valuables inside ( Guru Teg bahadur Jis Gurbani) and then RE-USING the SAME GOOD LOCK and relocking the warehouse..TREASURE HOUSE !!
11. The Raagmalla..comes AFTER the Mundawnni....just like someone leaving a "gift" at YOUR DOORSTEP..fater ringing the bell and being unable to enter yoru home..or running away after placing it there hoping you will take it inside (like the Trojans who dragged in the TROJAN HORSE the Greeks left at their Gates ). The Raagmala remains OUTSIDE due to the excellent Mundawnni lock..but kind hearted sikhs do read it..just becasue its there...its NOT GURBANI becasue it carries no Mehlla and has nothing of spiritual values...mostly mytholigical fantasy...that only saadhs and baabs can possibly love.
12. The NITNEM in the SGGS...is written in the Beginning pages of the SGGS. Japji Sahib...the REHRASS Sahib..and SOHILA SAHIB are in a SPECIAL CATEGORY right in the beginning of sggs before the Raags begin with Sri raag Mahalla Pehla.
13. The SRM formulators from various maryadas, smapardas, taksaals etc etc...got together in the early 1915 onwards to standardise a SRM. This was a HUMAN EFFORT - NOT GURU EFFORT. The SRM made it mandatory to read Japji, Jaap swaiyahs, chaupai in rehrass and sohila and Five paurees of Anand sahib. STILL the SRM Failed to be completley agreeable to ALL....the Taksals, akj jatha, various deras etc etc carried on with theri own maryadas....some adding this bani and another removing this bani...soem have arrills and jagmata shabads in rehrass..others read complete 40 paurees of anand sahib..etc etc..some ban meat..others say jhatka is ok...its a FREE FOR ALL simply becasue this is a MAN MADE DOCUMENT. The Guru Khalsa Panth can make and break this any time. ONLY THE SGGS CANNOT BE ALTERED IN ANY WAY. There cannot be any GURBANI left OUTSIDE the GURU...SGGS. The GURU is a sealed closed Bir. Period.
The GURU KHALSA PANTH and the SGGS...and KHANDEY BATTE DEE PAHUL are FOREVER...no danger form anyone...EXCEPT from SIKHS who DONT FOLLOW the SGGS in FULL and LIVE ACCORDING TO GURBANI in SGGS..that is follow what the GURU SAYS to the LETTER !!:happysingh::happysingh::happysingh::happysingh::happysingh:Bhai Daya Singh, Bhai Dharam Singh, Bhai Himmat Singh, Bhai Mohkam Singh and Bhai Sahib Singh BOWED to ONLY ONE GURU...GUru gobind Singh Ji...who instructed us to BOW to ONLY ONE GURU>>SGGS !! but we disobey HIM...and look elsewhere for "gurbani"....:happysingh::happysingh::happysingh::happysingh::happysingh: