On what basis does the author of Ancient India say that the original Vālmīki Rāmāyaṇa contained only 6,000 or 12,000 verses?

Question

In Ancient India, which served as a textbook for Class XI students in India during the 1980s, the author, Ram Sharan Sharma, makes the following claim about Vālmīki Rāmāyaṇa:

The two epics and the major Puranas seem to have been finally compiled by circa A. D. 400. Of the epics, the Mahabharata is older in age and possibly reflects the state of affairs from the 10th century B.C. to the 4th century A.D. Originally, it consisted of 8800 verses and was called Jaya Samhita or the collection dealing with victory. These were raised to 24000 and came to be known as Bharata, named after one of the earliest Vedic tribes. The final compilation brought the verses to 100,000 which came to be known as the Mahabharata or the Shatasahasri Samhita. It contains narrative, descriptive and didactic material. The main narrative which relates to the Kaurava-Pandava conflict may belong to later Vedic times, the descriptive portion might be used for post-Vedic times, and the didactic portions generally for post-Maurya and Gupta times.

Similarly, the Ramayana originally consisted of 12000 verses, which were later raised to 24000. This epic has also its didactic portions which were added later. As a whole the text seems to have been composed later than the Mahabharata.

In a more recent version of the book published by the Oxford University Press, the author writes:

Similarly, the Ramayana of Valmiki originally consisted of 6000 verses which were raised to 12,000, and eventually to 24,000.

On what basis does the author say that Rāmāyaṇa originally contained only 6,000 or 12,000 ślokas?

Answer 1

Could this be the source of the 12000 verse version of Ramayana?

https://www.jstor.org/stable/25210368

"The Oldest Record of the Ramayana in a Chinese Buddhist Writing" (K. Watanabe)

In the Mahavibhasa, the well-known commentary on the Jnanaprasthana of Katyayaniputra, there is a short passage which is of importance in the history of Sanskrit epic literature. The great commentary mentions, as an example of the contrast between Buddhist and non-Buddhist books, the size and contents of the Ramayana. The following is a literal English translation from the Chinese version by Yuan Chwang: "As a book called the Ramayana, there are 12,000 slokas. They explain only two topics, namely : (1) Ravana carries Sita off by violence, and (2) Rama recovers Sita and returns. The Buddhist scriptures are not so simple. Their forms of composition and meanings are respectively immeasurable and infinite." ................... Laying aside this difficult question, we have reason to believe that the Mahavibhasa must have existed at least half a century before the time of its older translation. Kumarajiva began his work of translation in 402 A.D. The date of the translated sastra, therefore, cannot be later than 400 A.D., and the Vibhasa therein described belongs naturally to an older time. Though we assume the latest possible date, still we cannot doubt its existence at the end of the first half of the fourth century; and it may be dated much before that. In any case, the description in the Mahavibhasa is -- along with the well-known Ramayana portion of the Mahabharata -- the oldest literary record of the Ramayana yet known, and its clear mention of the size of the epic is especially valuable. ................... This shows that the Ramayana, even in the time of Vasubandhu, who, as is most likely, flourished about 420-500 A.D. was a popular book and widely known, even among the Buddhists.

Answer 2

Actually, it is said in the Yoga-vasishtha that the Ramayana (as the Maharamayana) once consisted of 100,000 verses:

20. O sinless saint! The puranas also though they agree in the main substance, are so full of interpolations, that they have been greatly multiplied in successive ages.

21. I remember also many historical works, which have been composed by authors learned in the vedas in the succeeding ages.

22. I have the recollection of the other wondrous composition of legendary accounts, under the title of the Maharamayana a work comprising one hundred thousand slokas or tetrastichs, and replete with sound wisdom.

23. This work presents the conduct of Rama for the imitation of the men, and sets the misbehaviour of Ravana to the opprobrium of mankind. This precept contains the essence of all wisdom, and serves as the luscious fruit of the tree of knowledge, placed in the palm of all people.

24. This work is composed by Valmiki, who will compose some others also in time; and these you will come to know, when they will be presented to world in time (as I have known them before hand by my foreknowledge of things, gloss).

25. This work whether it is a composition of Valmiki, or the composition of some other person, is published for the twelve times, and is now going to be almost forgotten by men.

26. The other work of like importance, is known under the name of Bharata; I remember it to have been written by Vyasa at first, but is becoming obsolete at present.

Imho it is hard to understand the true scope of recurring scriptures, their true extent and their redacted editions.