You are asking a factual question. One place to look for citations of facts on the issue is in the extensive footnotes of the book The Hindus: An Alternative History[1] by Sanskrit scholar Wendy Doniger. The book points out that the Harappan inscriptions depict several animals that are mentioned nowhere in the Vedas, while the Vedas in turn mention (in writing) several animals that appear nowhere in the Harappan inscriptions. In other words, the Vedas were composed in a region of Asia with different animals, because of different climate, from the region where the Indus Valley civilization arose. The Vedas also describe many aspects of an ancient lifestyle that was certainly not centered around cities in a river valley like the valley of the Indus. There are multiple lines of evidence to show that the Vedic culture and the Harappan culture were distinct and arose in different parts of south Asia.

The historiography of India is a very complicated issue, in large part because of lack of written records in key phases of the development of civilization and religion in India, and also because historical claims about India are tightly bound up in political claims about current Indian politics. A Google search on "Indian historiography" (a search I just did) will disclose some of the competing claims.

[1] http://www.amazon.com/Hindus-Alternative-History-Wendy-Donig...