Some quick notes in reaction to your query: 

It is a widely accepted cliché that "the Vedas are eternal and apauruṣeya" and another cliché, equally widely accepted by both traditional and modern, Indian and non-Indian, scholars is that this is essentially (!) THE Indian view on the Vedas. At some point in time, indeed, the "irrational" view of the nitya and apauruṣeya Veda became dominant, and the theory of elevated but basically "human" authors disappeared from view in "orthodox" circles (just as the view of an originally basically "human" Jesus Christ advocated by Arius made in the course of time place for more "irrational" positions such as Trinitarianism which implies the anādinidhanam divinity of Jesus in Christianity?). This means there was an earlier time that the view of a nitya and apauruṣeya Veda was not dominant or evident. Even if we limit ourselves to the six so-called "orthodox" schools of Indian philosophy we find that widely divergent views were held about the nature and (extent of) authoritativeness of the Vedas -- and on the question whether the Vedic texts had or did not have authors: Sāṁkhya is severely critical of the Vedas and Vedic ritual (Houben 1999); Nyāya makes efforts to prove that the Veda is not apauruṣeya but pauruṣeya: deriving from a Puruṣa, namely God (Chemparathy 1983); the school of Aitihāsika interpretation of the Rgveda did not survive but interpreted the subject matter of hymns often in terms of references to human or divine,“historical” personalities (E. Sieg 1902). Not much of their views is preserved, but it is likely that the authors of the hymns were also regarded as “historical” personalities; in Vaiśeṣika, although theism overtook later on, there is no early systematic commitment even to God but to the Ṛṣis and their knowledge (even Praśastapāda accepts, apart from pratyakṣa, laiṅgika and smṛti, only ārṣa as another category of reliable knowledge, vidyā, in contradistinction to four forms of avidyā) >From Vaiśeṣika-sūtra (VS)6.1.1 buddhipūrvā vākyakṛtir vede we can infer the position that the composition of Vedic texts is preceded by thinking, and hence a creation by individuals, esp. the seers, although Candrānanda’s commentary forcefully tries to interpret the plural as honorific and the reference to the author of the Veda as a reference to Maheśvara (Houben 2019, pp. 198-199); in the system of Yoga (Yoga-sūtra etc.) the Veda and God have marginal roles, as for the latter i.a. in an optional way to the ultimate Yogic goal (A. Nugteren, God as an alternative, Leuven, Apeldoorn: Garant, 1991). Hence, we are left with only Pūrva-mīmāṁsā and Vedānta as fully and originally committed to the Vedas as sources of ultimate knowledge, an irrational position which Mīmāṁsakas such as Kumārila brilliantly tried to defend rationally by arguing for a nitya and apauruṣeya Veda. Somewhere in Alexis Pinchard’s Les langues de sagesse dans la Grèce et l’Inde anciennes (2009, based on a thesis defended in 2005) the author describes how there is an 'inflation' in the sacred status of Vedic and Sanskrit, an ‘inflation’ that can be easily traced back to its earlier stages. At first, the “secret names or footsteps of the cows” are preserved in ‘human’ hymns addressed to the gods. Subsequently, the entire ‘human’ hymns, skillfully composed by trained poets, acquire the status of divine texts which through their metre etc. are demarcated from all other language use, including the comments and explanations of difficulties associated with these divine texts. The next stage is the acquisition of divine status of both the hymns and their explanations, the stage reflected in the dictum mantra-brāhmaṇayor veda-nāmadheyam “Mantras and Brāhmaṇas have the designation ‘Veda’ ” (Āpastamba Śrauta-sūtra 24.1.31). The auxiliary disciplines such as grammar, etc., which develop in order to bridge the increasing distance between the language of the Veda and even the polished language of daily life, are the next candidates to receive divine status; the last observed stage is the attribution of divine status not only to Vedic literature and its auxiliary disciplines but to the entire Sanskrit language, a view which we find already clearly formulated by the 5th century grammarian-philosopher Bhartṛhari, but which remained in his time far from uncontested (Houben 1996b). This does not detract from the de facto role of classical Sanskrit as a language to the co-production of which Buddhists contributed importantly, a philosophical and literary lingua franca (Houben 2018 “Linguistic Paradox and Diglossia”).  

Best, 

Jan Houben