I was just going through some old journals of the Music academy and came upon the article on Abheri by Amy Catlin, the American musicologist. I do remember having read this article some years ago and a reference to this by my good friend Srini Pichumani on Sangeetham. Fortunately I chanced upon this yesterday and thought I could share some of the important points not discussed earlier.
1. Govinda's Sangraha Chudamani gives the dhaivata of Abheri as a Trishruti which is higher than the suddha dhaivata and lower than the chatussruti dhaivata.
2. Coming to nagumomu Amy Catlin quotes two sources - The Walajapet manuscripts and Vina Kuppayyar's notebooks where the raga name is not mentioned at all. Sambamoorthy has identified a total of 83 such ragas where the names were not mentioned and Abheri is one of those.
3. The first known publication of nagumomu with swara notation was the Sangita sarvartha sara sangrahamu the raga for nagumomu is mentioned as Nagavarali a janya of mela 8. This is an 1885 publication. Tachur Singaracharlu in their 1877 publication also mention nagumomu as Abheri but without any swara notation. Chinnaswami Mudaliar's Oriental Music in Staff notation (1892) was to have had nagumomu as per a list of songs circulated in advance soliciting money, but was never printed.
4. The first known performer of nagumomu was Sarabha Sastri on the flute who was a disciple of Manambuchavadi Venkatasubbayyar.
5. The reference to Madurai Pushpavanam having sung Abheri is referred from an eyewitness account narrated in Rangaramnuja Iyengar's book. (This is probably the reference Ram was thinking about when he made the comment in the earlier post) Rangaramanuja Iyengar has also said that Pushpavanam sang the trissruti dhaivatam. (My personal view and more or less what Ram had echoed earlier is that this trissruti dhaivatam could have easily morphed into the chatussruti dhaivatam when Musiri sang it. But more practically a trissruti dhaivatam would have sounded more like an off sruti chatussruti dhaivatam to a modern ear!)
6. Maharajapuram Viswanatha Iyer was the next to sing nagumomu. He was inspired by Pushpavanam. He also borrowed from Hindustani music and consistently mixed Bimpalas in his renditions. This could be another direct result of nagumomu acquring its modern form.
7. By 1930 the modern nagumomu had become very popular. The raga lakshana discussions in the Academy were more conservative and ruled that Abheri was a janya of the 20th mela. But musicians like Tiger and Muthiah Bhagavatar commented that that d2 should be allowed in tune with times.
8. Among other things the conclusion of the article says "it is possible for two entirely different forms of the raga to exist today, each associated with different compositions, and for a variety of forms to be permissible in the performance of nagumomu"
The only thing missing in the above article is any reference or mention of Devagandhari.