Argthtjtr

Rig Veda presents complete set of modern numerals

1. ekam


2. dvi


3. tri


4. catur


5. panc


6. sasti


7. Sapt


8. asta


9. navam


10. dash


11. ekadash


12. dvadash

.....etc leading to sahastra (1000).

Yet modern scholars hold that the modern numeral system originated in India in 5th-7th century AD. Why it is so? Even the conservative dating of Rig Vedic Sanhita is 1200 to 1500 BC. Is not it a denial of the depth of Indian historicity?

I believe your question arises from a misconception of numerals.

A number is a more-or-less abstract (and hard-to-define!) entity used for counting, enumerating, calculating and so on. Numbers have names in every language.

A numeral is a written sign used to represent a number or part of a number. The number four is always the same, but there are many different numerals which can represent the number four, besides the most common one "4". Additionally, the number which is called "four" in English has others names in other languages.

It is agreed that the Rig Veda was preserved and transmitted only orally for very many centuries, even after the development of writing in India, and was probably not written down before the development of the Indo Arabic numerals^{1, 2}. Its unique language, including the words that represent numbers, can be represented in various scripts, but the original composition of the Rig Veda long preceded any written signs used to represent it.

Therefore at the outset, it is apparent that while the Rig Veda conceptualises numbers and gives names to represent them, mentioned in your question, it cannot be said that the Rig Veda directly originated numerals as such, because numerals are written signs. To discover the origins of numerals, we should primarily study writing systems.

The Indo-Arabic numerals² used in English and many other languages (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) are thought to have been developed in India over several centuries, but by 7th century AD. The great mathematician Brahmagupta is credited with developing methods to calculate using zero as a number, effectively enabling the use of a positional system that allowed all numbers to be represented (in base 10) with only 10 numerals, making the developing Indian numeral systems (the actual signs used varied) that used this type of notation highly practical for calculating.

This modern numeral system developed directly from the Brahmi numerals which are part of the Brahmi script:

It can be seen here that the Brahmi numerals had to proliferate beyond ten signs because, without a marker for zero, and the positional system it enabled, it was not possible to distinguish between large and small numbers without using new signs.

When scholars date the development of the modern numerals, which I have given a very brief outline of above, they are describing the evolution of a series of written signs, rather than the origin of numbers themselves or ways of naming them. Mathematicians such as Brahmagupta may have developed their writing methods with the help of mathematical skills and knowledge drawn from ancient sources including the Rig Veda, but the Rig Veda cannot be said to have contained those writing methods (numeral systems) during the thousands of years it existed before being written down.

¹ See for example: Rigveda on Wikipedia.
² See for example: Indo-Arabic Numerals on Wikipedia. These numerals are called in English the Arabic numerals or Hindu-Arabic numerals or Indo-Arabic numerals for historical reasons - although they were indisputably developed in India they were transmitted to the Arab world and used extensively by Arab mathematicians, and thence eventually came to be used in Europe.