Vedas, as we believe are words of God so they should be static, but, I think Rigveda has been corrupted. E.g., Nirukta 7:8 talks of a verse offering an oblation to Vishnu and Agni but the verse is not present in Rigveda anywhere.
Does this mean Vedas aren't well-preserved as thought and the contents changed over time?
Are Vedas well-preserved or not?
They are extremely well preserved. It is not just orthodox Vedic scholars who agree with this but even Western Indologists agree. Michael Witzel, who is the most profound and influential Western Indologist of current and recent times, Wales Professor of Sanskrit at Harvard University, and the "king" of the modern iteration of the Aryan Invasion Theory, says this:
“Right from the beginning, in Ṛgvedic times, elaborate steps were taken to insure the exact reproduction of the words of the ancient poets. As a result, the Ṛgveda still has the exact same wording in such distant regions as Kashmir, Kerala and Orissa, and even the long-extinct musical accents have been preserved. Vedic transmission is thus superior to that of the Hebrew or Greek Bible, or the Greek, Latin and Chinese classics. We can actually regard present-day Ṛgveda recitation as a tape recording of what was composed and recited some 3000 years ago. In addition, unlike the constantly reformulated Epics and Purāṇas, the Vedic texts contain contemporary materials. They can serve as snapshots of the political and cultural situation of the particular period and area in which they were composed. […]as they are contemporary, and faithfully preserved, these texts are equivalent to inscriptions. […] they are immediate and unchanged evidence, a sort of oral history ― and sometimes autobiography ― of the period, frequently fixed and ‘taped’ immediately after the event by poetic formulation. These aspects of the Vedas have never been sufficiently stressed […]” (WITZEL 1995a:91).
No, they aren't. This becomes evident when you look at the mantras of Sāmaveda which are usually sourced from the Ṛgveda. There are about 75 (yoni) mantras in the Sāmaveda without the original Ṛgvedic source. And some Sāmagāna mantras, that are actually sung, without the corresponding yoni (source) mantras.
1. Introduction
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Sāma Veda Samhita, in reality, has two parts. The first part consists of the (source) text of the rik mantras which are to be sung. It is properly called Sāma (yoni) mantra samhita. The second part of Sāma Veda gives the text of mantras which are actually sung. This part is called Sāmagāna text or text for singing. Thus every mantra in the first part, is expanded to yield one or more Sāmagāna mantras. Note that there are also several Sāmagāna mantras (mantras which are sung) which do not have a source rik mantra.
3. Sāma Veda and Rig Veda: Connection
It was mentioned that the text of most of the Sāma Veda verses is in Rig Veda. The complete recension of Rig Veda available today is Shākala. Of the 1875 Sāma yoni mantras, 1770 are in Shākala recension of Rig Veda. Another 29 verses can be traced to the mantras of the Khila sūktas of Rig Veda and some slightly modified versions of the mantras of RV. The remaining 76 mantras in Sāmaveda presumably are from the recensions of Vedas which are lost today.
Each chapter or adhyāya takes verses from different Mandalas of the Rig Veda. For instance, the first nine mantras of the first adhyāya of Sāma Veda having ten mantras have same text as the following RV mantras: 6.16.10, 6.16.1, 1.12.1, 6.16.34, 8.84.1, 8.87.1, 6.16.16, 8.11.7, 6.16.13. The tenth mantra has no corresponding RV mantra.
9. Some Well-known Sāmagānas
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2. Subramaṇya Sāma: Begins with ‘subrahmaṇyom’; not based on any SV yoni mantra or RV mantra.
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3. Bṛhat Sāma: Not based on RV or SV yoni mantra.
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6. Mahāvairāja Sāman: Has no source SV mantra text.
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11. Go-Sāma: Has no known source mantra.
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