When speaking about the Nadi we only seem to know the Nadi written for individuals kept by Nadi readers and retrieved when a seeker steps before them in search of his past, present, and future.
https://agathiyarvanam.blogspot.com/2014/01/all-about-nadi.html
But the art and technique of writing on palmyra leaves were not solely used for this purpose of prediction or astrology. The Thamarai Noolagam in Chennai is said to house an extensive number of books on the songs of Siddhas that were originally written on palm leaves. Many ancient texts and scriptures that have been written on these leaves are lost over time due to deterioration lack of care and other reasons. Many have been destroyed or burnt. For instance, we are told that we have in our hands only about 3000 plus songs of Saint Arunagiri among the 16000 know to be sung by him. It is said that the sea swallowed them indicating the floodwaters had swept them away. It is said that many scrolls were bought from locals who did not know their value and taken away to foreign lands. We are told many are still hidden in secret chambers and caves waiting for the right moment to be revealed.
Dr. Mandayam Kumar from the Siddha Medical Research Institute in Bangalore, in an article of his, "Siddha Agastya - Foremost of the Siddhas" based on findings from an ancient text attributed to Lord Muruga entitled "Prapancha Kaandam" mentions that it was possible to find out details about Agathiyar during the course of literary research on the Siddha medical sciences in a Tamil manuscript written on palm leaves about 3,000 years ago. Agathiyar narrated the contents while Pulastyar recorded it.
The Siddhas recorded their knowledge on palm leaves after extensive discussions held in Alagan Kulam and presented them to Lord Dhakshinamurthi for his perusal. This included the 64 kinds of learning, 18 Puranas, 96 tatvas, and 48 branches of scientific knowledge. The entire literature in Tamil came to be called "Siddhaveda".
Tavayogi who led me to all the temples stipulated by Agathiyar that I should visit in my Aasi Kaandam and more that he told me I should see including caves and samadhis that he added on as I followed him, chose to deviate momentarily bringing me hurriedly to see King Sarobhoji's collection at his palace that is now the Royal Palace Museum in Thanjavur. Trying to beat the closing time, he hurriedly showed me numerous Nadis or Suvadis housed at the famous Saraswathi Mahal library, telling me he had been there in his early days studying them. When we returned to his Kallar ashram he brought out many Nadi scrolls that were in his possession. Many had been passed to him when his name appeared in them. He showed me the various forms of writings on them that carried a name each.
We learn from the website https://www.tamilheritage.org/ the Tamil Heritage Foundation has done extensive research and finding in this area seeking them out and digitalizing them in the interest of preserving such a precious heritage for future generations. Read more at http://www.madrasmusings.com/vol-27-no-6/tamil-across-the-oceans/
We find much material on Dr. K. Subashini's YouTube Channel too at https://www.youtube.com/channel/UC9N9w5u2NhnX4OV6CKu5mvA
While much effort is placed by such institutions in preserving this heritage by digitalizing, a member of the public has taken the sole endeavor to rewrite existing texts onto palm leaves.