What are the requirements to be Indian in Assam state

Four million people in northern India have effectively lost their citizenship after their names were left out of a national database of registered citizens. The list now includes only those who were able to prove they were in Assam state before 1971. For the people who've been left out of this list, there's fear they might become stateless or even face deportation. Narendra Modi's government argues they could NOT produce valid documents. But Indian leaders have assured them there won't be any immediate deportations and people can appeal to have their names registered. This all goes back to Bangladesh's 1971 war of independence. That's when hundreds of thousands of people fled to India to escape the fighting. Many of them settled in the north-eastern part of the country, mainly in Assam. So, have they become stateless? And will this create further division?