The first link
explains van Putten’s use of the term ‘Poetic Arabic’. As I understand it he’s saying that it (i.e. the language that pre-Islamic poetry is assumed to have originally been composed in) may have been the basis for Classical Arabic but definitely not for the Arabic of the Qur’an.
So for the past century or so, the status quo opinion has been that the Quran was composed in a language which has gotten so many different names, that it can be rather confusing: "The ʿArabiyyah/The Pre-Islamic Koine/The Poetic Koine/Classical Arabic/Pre-Classical Arabic, etc. etc." The exact name an authors gives this language kind of depends on the theoretical framework they work from, but for all of the scholars working on this, whatever term they used, they agreed that this meant that the language of the Quran was identical to the language of the Pre-Islamic poetry, which in turn is quite close to the language that we call "Classical Arabic" today. While it is perhaps a terrible idea to introduce yet another term, I'll do it anyway: Let us call this "Poetic Arabic" for now.
Over the past two years, I have built up the case that the language of the Quran was not composed in Poetic Arabic, but rather a vernacular language -- likely the language spoken in the Hijaz at the time of the revelation. I call this "Quranic Arabic"
The Quran was previously the only evidence for Poetic Arabic that stemmed unproblematically from the 7th century. Because of its language being identical, it suddenly did not seem unlikely that the pre-Islamic poetry from around the 6th century would also be composed in this period. The poetry itself only gets put into writing about two centuries later, and there is no a priori reason to assume that these are genuinely from that early a period, but the Quran anchored it. With the Quran being composed in a different language, that anchor has now been lifted.
The absence of a language identical or close to Poetic Arabic in the pre-Islamic epigraphic record need not mean that a form of Arabic with a functioning case and mood system did not exist at all as a spoken language in the 6th and early 7th century. The modern Najdi dialects developed from a branch of language which at least had tanwīn, something that Quranic Arabic had already lost by that time. The fact that the medieval grammarians saw the best Arabic to come from the eastern dialects (i.e. Central Arabia/Najdi tribes), and that even today the oral poetic traditions of these dialects retain meters similar to Poetic Arabic poetry, where word-final consonants, at least in some contexts are treated as if they are followed by final short vowels (= the case/mood vowels) is a tantalizing indication that there is something going on in these eastern dialects.
As it stands, however, nothing that is even remotely like Poetic Arabic has shown up yet in the Pre-Islamic epigraphic record; and it perhaps never will. We do not know if the ancestral language of the Najdi dialects had a writing system, and its silence in the epigraphic record might suggest that they didn't. But alternatively, we might simply be looking in the wrong place or we haven't looked yet.
What is clear, however, is that the variety was not used for writing (and presumably also not for speaking, or even poetry) along the Hijaz, and the Levant, where forms of Arabic have been found, none of which look like Poetic Arabic.
But that Poetic Arabic was not a spoken language in, e.g. the Hijaz around the time of the Islamic revelation, does not mean it wasn't a Epic Greek-like special inter-tribal poetic register. The Islamic tradition certainly gives us the impression that this was the case. There is a great collection of Pre-Islamic and early Islamic poetry attributed to different tribes, and they all display more-or-less the same language. However, there are two issues that need to be addressed before we can start to develop the idea of Poetic Arabic as an inter-tribal archaic poetic register. First there is the problem of classicization, and second there is the issue of authenticity.
Pre-Islamic poetry was only really recorded in the 2nd and 3rd Islamic centuries as part of an effort of codifying a high language which would then become "Classical Arabic". Clearly these codifying efforts must have had a rather homogenizing effect -- and comparing the linguistic features of pre-Islamic poetry to the Quranic reading traditions, or even the descriptions of the early Arabic Grammarians such as Sibawayh, give the impression that the pre-Islamic poetry must have been heavily classicized, and the apparent linguistic unity and the similarity of Poetic Arabic to Classical Arabic might be completely an artifact of the grammatical tradition. An argument I tried to make in my IQSA blogpost. If there was an inter-tribal poetic register, it seems likely that there was considerable (but probably not insurmountable) dialectal variation within this register.
The issue of authenticity is one that I am not sure how to go about answering. If we blindly trust the Islamic tradition, we must believe that people close to the prophet indeed composed poems in Poetic Arabic -- a language which they almost certainly did not speak as their first language. But why should we trust these accounts? The poetry was written down much later, and considering the enormous amount of status Poetic arabic cum Classical Arabic comes to acquire around the time these texts get recorded, combined with the belief that the Quraysh spoke impeccable Arabic and that the Quran was revealed in the language of the Quraysh make any of these attributions somewhat suspicious.
This does not mean that the poems composed in Poetic Arabic contain no authentic references to Pre-Islamic Arabia, they certainly do (see my IQSA blogpost for one such an example); But just because the poems might be authentically pre-Islamic need not mean that all poems attributed to the pre-Islamic and early Islamic period are to be attributed to the authors they are attributed to, nor even that the whole of the poems are authentically pre-Islamic. This is an element which surprisingly often gets overlooked by people who want to think of Poetic Arabic as a "Poetic Koine". If Zwettler is correct that Poetic Arabic really was, like Epic Greek, a formulaic poetic register with a tradition that trained poets could draw upon to semi-recall/semi-improvise the "Epic" Poems, it is perfectly possible that poems that were composed in the second century could still contain figures of speech that date back hundreds of years. This is exactly what we find in the Homeric epics, verses that are evidently extremely ancient, more ancient than even the events, e.g. the Iliad talks about, side-by-side with verses that must post-date the events described in the Iliad by hundreds of years still (due to the mentioning of materials that did no exist yet, etc.).
That there is some amount of authenticity and ancientness to these poems at the time that they get written down, however, is clear because they people writing commentaries on the meanings of the poems seem to often be completely clueless about some elements of their meaning, while within the context of the poem, it seems quite clear that the composed was aware of their meaning.
Let us grant that Poetic Arabic was indeed a intertribal archaic register that enjoyed considerable cultural prestige. This still would not mean that the written language of the early Islamic period, nor the language of the Quran would also automatically be in that language. Among Arabists, there seems to have been a consistent idea that if there was a literary register for poetry, this would automatically dictate that this would have become the written language. This of course does not follow at all. One need only look at the literary languages of ancient Greece, none of which were similar, or even particularly close to Epic Greek nor was that the standard they were aiming for. Examining the early Islamic papyri and inscriptions, it is linguistically very similar to Quranic Arabic and, in fact, to literary Christian Arabic -- but rather further removed from Poetic Arabic. Only when the Arab grammarians set out to codify the Classical Arabic language, we start to see a noticeable change in the language used, at least in literary works (non-literary texts certainly lag behind, and early Christian Arabic does not seem to evidently make the adjustment any time soon pace Blau, who seems to think Christian deviations from Classical Arabic are just failed attempts to write Classical Arabic rather than succesful attempts to write the pre-Classical literary register). The fact that pre-Grammarian copies of works such as Ibn Wahb's Hadith collection on Papyrus are decidedly pre-Classical in orthography and language, clearly show that the crystallization of this language, even in literary works only took place due to the efforts of the grammarians.