It’s almost like waiting for a seismic event that has been prophesied. As the New Year approaches, Assam is bracing for a precipitate moment in its political history: the first draft of the updated National Register of Citizens (NRC) is to be published on December 31. The Supreme Court-monitored process, which will enumerate and name all Indian citizens in Assam, is the first update since 1951.

It will be an event that brings together, in one mekhela weave, most strands defining Assam politics—history, demographics, ethnicity, religion, language—and spins an unpredictable tale going forward. As crucial as those named and included as citizens will be those who get left out. No light is being allowed in through the cracks, but perhaps there will be lakhs of them. Once the draft is published, those left out can file objections, which will be heard, before a final draft takes shape.

The 1951 NRC was based on that year’s census. The difference between the two—the exercise is restricted to Assam at present—lies in the layers of...