Wherefore art thou, aberil?

[ReneZ]

Indeed, but all the ones I checked are in Northern France (North of Paris). This is the area proposed by Thomas Sauvaget (You are not allowed to view links. Register or Login to view. quoted in a parallel thread).
 
Jean Ruel, whom I mentioned before is, from Soissons, very much in that region.

So we have Switzerland and Occitania for Aberil, but so far no Octembre, or Yong.
And we have N.France for Yong, Augst, Octembre, but no Aberil.

[Koen G]

So we have Switzerland and Occitania for Aberil, but so far no Octembre, or Yong.
And we have N.France for Yong, Augst, Octembre, but no Aberil.

Thanks, this overview helps.

Wouldn't the most likely explanation be that aberil is an aberration?

[nablator]

So we have Switzerland and Occitania for Aberil, but so far no Octembre, or Yong.

Occitan is Abril or Abrial.

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[Koen G]

I put some of the locations from You are not allowed to view links. Register or Login to view. I mentioned before on a map (very likely containing mistakes), and this is what I got for Octembre:

   

(I repeat, this is likely to contain mistakes and would need to be checked).

[ReneZ]

Occitan is Abril or Abrial.

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But how about the late middle ages, and perhaps regional variation? (Real question - I don't know).

[nablator]

But how about the late middle ages, and perhaps regional variation? (Real question - I don't know).

I don't know a medieval occitan dictionary.

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Here they have abriel, abril, avril:
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Etymological dictionaries have most of the ancient variants:
You are not allowed to view links. Register or Login to view. --> abril, abriol (1475, Fazy)

[ReneZ]

Thanks! 

In all of the numerous examples, there is great variety in what comes after "br", but I have not seen a single case where there is anything between the "b" and the "r", so that certainly makes occitan more doubtful.

[R. Sale]

While it may seem contrary to expectations, rather than trying to pin this all down to a specific location, what if some of the actual words used to name the months were selected because of their linguistic diversity?

[Mauro]

I got this article in my academia.edu feed today: You are not allowed to view links. Register or Login to view.

It has no direct relevance to the VMS or to 'Aberil', but it discusses the challenges posed by the orthography and spelling of Medieval manuscripts and I found it interesting, ie.:

However, historical documents are difficult to analyze. They were handwrit- ten on skin (parchment) or paper. Over centuries, portions of those documents deteriorated physically which makes their writing difficult to decipher, even with help of advanced scanner and optical character recognition software. The writers of those documents are typically not known by name, and the context of their writing is often unclear from our contemporary point of view. European orthography was not standardized until about two centuries ago. In medieval Europe, manuscripts were often written to be read out loud rather than being studied quietly; the general public (including even some members of the political leadership) was mostly illiterate. Writing was restricted to impor- tant matters only, since the writing material was expensive to obtain. Moreover, the medieval world was to a large extent regionally confined, with only little trans-regional mobility, such that many regional customs, habits and dialects were preserved. These factors also contributed to the delay of standardization in orthography.

I would add that many European languages did not achieve a standardized orthography to this day (ie: just in Italy there are a couple dozen full-fledged languages whith no agreed-upon orthography and scant historical documentation).

[Jorge_Stolfi]

In all of the numerous examples, there is great variety in what comes after "br", but I have not seen a single case where there is anything between the "b" and the "r", so that certainly makes occitan more doubtful.

Some languages and scripts do not have consonant clusters like "br", and their speakers will insert vowels into them.  Japanese native speakers, for example, would transcribe and pronounce "abril" as "a-bi-ri-ru" or "a-bu-ri-ru".

In Northeast Brazil, a railroad tie is called "chulipa" ("shoo-LEE-pa").  That is what the local workers heard when the British engineers who built the first railroads in the 1800s said "sleeper".  The "sl" cluster is very rare in Portuguese, and never word-initial.

BTW, "April" is written "abril" in modern Portuguese and Spanish too.