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?