Rangpur, Shivpur, Sibsagar, Sivasagar
The district's history page gives the town four names in about three centuries: Rangpur while it was the Ahom capital, Shivpur until the end of Ahom rule, Sibsagar after the Treaty of Yandaboo, and Sivasagar, the spelling the district administration uses on its website today. The contact address on that same site still says sibsagar.
For a business here that is a small, practical point. A customer may type either spelling when they write first, and a reply inside the 24-hour window can simply use theirs. A template is fixed text that Meta approves as written, so pick one spelling, the district's, and keep it in every address line, dispatch note and booking confirmation you submit.
The same goes for language. Replies can follow the customer into Assamese. The paperwork a mill, a supplier or a guide sends after a quiet spell, the dispatch note, the invoice, the tour confirmation, is written once, in English or Hindi, and reused.
