Neutral Singh,

"But one that can never be manipulated is Granth Sahib Ji... the perpetual Sikh Guru." - Neutral Singh

Allow me to shed some light on this misconception of yours.

Guru Arjan Dev “compiled” (i.e., collected “past” scriptures) and had it written by a “scribe” Bhai Gurdas.
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

It was originally called “Adi” Granth (or, Pothi Sahib) NOT Guru Granth Sahib.

Guru Gobind Singh undertook preparation of the “new” edition of “Adi“ Granth, which eventually became the “Guru” Granth Sahib, scribed by Bhai Mani Singh.

The “eternal” Guru Granth Sahib, "which can never be manipulated", had its "beginning" in 1604, and completion in 1706, yet it is not called the eternal/timeless until 1708, hence overlapping five Gurus from Guru Arjan Dev to Guru Gobind Singh from its inception.

Why didn’t Guru Arjan Dev pronounce Adi Granth the “eternal/timeless” Guru in 1604?

What was the status of this holy book during the periods 1604-1706-1708 i.e., from being Adi Granth to Sri Granth, before finally declared the Guru Granth Sahib?

Why did it take 104 years for Adi Granth to become Guru Granth Sahib?

So, the Guru Granth Sahib:
Though "eternal" had its beginning in 1604;
Though "never manipulated" was altered/modified (apparently to remove some unauthorized texts) and dictated again by "another" Guru, Gobind Singh in 1706;
And finally, though "perpetual", written in 1604, yet did not become Guru until 1708.

Over to you.

Regards
Rajs