On Quora, I have seen many people (mainly ISKCON priests) say that Shiva Purana was "adulterated by Shaiva kings" or something along this line. Is this true or false?
The question title and the actual questions appears different to me.
If you are talking about authenticity, is n't that very obvious?
Shiva Purana is definitely authentic. All major puranas mentions it as one of the puranas.
But, if you are talking about interpolations or adulteration done to a text, then that is definitely a high possibility.
The problem with puranas is the poor state of textual basis. The Puranas were not well preserved and could have some or heavy amount of interpolations.
The Puranas which have some commentary traditions like Gita, Bhagavata, Vishnu Puranas, chances of adulteration are less. Others could have interpolations like Skanda Purana etc..
This paper [ Harimoto, K. Indo-Iran J (2006) 49: 23. https://doi.org/10.1007/s10783-005-4913-9 ] talks about the Skanda Purana which was discovered which could be dated to 810AD Nepalese version. And it is quite different from the current Skanda Purana version available.
In fact verses, verses cited by Dharmanibanda authors from 12th century to 14th centuries were considered psueo-quotes till they were found in the old Nepalese manuscript, but not the current one.
In https://books.google.co.in/books/about/Origin_and_Growth_of_the_Pur%C4%81%E1%B9%87ic_Text.html?id=CLN0F7GGecsC&redir_esc=y Hans Bakker analyses how Puranas get corrupted over time with talking example of Skanda Purana.
The earliest known recension (S) preserved in Nepalese manuscripts can be dated to before the date of the oldest manuscript, i.e. to before 810 AD.
Most early testimonia of a Skandapurana can be identified as re- ferring to (a recension) of the text that we are studying, whereas works styled khandas of the Skandapurana' can be shown to have come into existence from the second half of the 12th century onwards. 2 In the end, they virtually replaced the original text. The latter survived, though ap¬ parently as good as forgotten, in the north-eastern part of the subconti¬ nent, but was forced, in order to do so, to pass itself off as merely an¬ other part of the elusive ‘ Skandapurana with the name of ‘ Revakhanda' or ‘ Ambikakhanda
This Nepalese version became altered and cut down in some places, but on the whole much enlarged in two later re¬ censions, which were handed down in manuscripts as the Revakhanda (R) and Ambikakhanda (A) of the Skandapurana. The only manuscript of the R recension dates from 1682, while the four manuscripts of the A recension are all later (and more corrupt). It seems, however, that a recension closely related to the hyparchetype of the R and A recensions was known to Laksmidhara, the author of the Krtyakalpataru, which means that this redaction was in existence in some form before 1100 AD. It must also be noted that R and A roughly follow the Nepalese S recension with occasional omissions and additions 2 until chapter 162
A long section of the chapters added to the core text of S by the R and A recensions deals with various stories of saiva mythology and ritual. These chapters are to be found at the beginning of where R and A start adding a large amount of new material. It is a distinguishing feature of these extra chapters that while the speakers formally remain Sanatkumara and Vyasa as before, the actual stories are often told by Siva to Devi. Some of these narrative parts focus on Devi’s desire to have children, and reading these passages one is tempted to speculate on whether this is the reason why the name Ambikakhanda was given.
He observes new chapters that were added:
1 The birth of Ganesa ( vinayakotpattih ) 2 The story of Siva’s ashes ( bhutyutpattih ) 3 The feast of Bhairava and Udakasevika, including the story of their birth ( utpattih)
So, in conclusion we can say Shiva Purana is authentic, but how much of it was subjected to interpolation can't be said unless a thorough study is done based on old manuscripts as in the case of Skanda Purana.
Yes, the Shiva-Purana is of course authentic. The following part of the Padma-Purana (Swarga Khanda) is well accepted in our tradition :
According to Suta, all the Puranas are nothing but the mediums through which Sri Hari manifests himself---Brahma Purana is said to be the forehead of Sri Hari, Padma Purana is said to be the 'heart' of Sri Hari, Vishnu Purana is said to be the 'right arm' of Sri Hari. Shiva Purana is said to be the 'left arm' of Sri Hari. Srimad Bhagavata is said to be his 'thigh', Narada Purana is said to be his 'navel', Markendeya Purana is said to be his 'right-foot'. Agni Purana is said to be his 'left foot', Bhavishya Purana is said to be his 'right-knee', Brahma Vaivrata Purana is said to be his 'left knee'. Linga Purana is said to be his 'right ankle', Varaha Purana is said to be his 'left ankle', Skanda Purana is said to be the hair on the body of 'Sri Hari. Vamana Purana is said to be his skin. Kurma Purana is said to be his back. Matsya Purana is said to be his stomach. Garuda Purana is said to be his bone-marrow. Brahmanda Purana is said to be his bone. So, all the Puranas being manifestation of different parts of Sri Hari's body are very sacred and capable of bestowing salvation.
Who will dare to brand the left arm of Sri Hari as unauthentic?