The RBI stated that it is possible to have two or more banknotes with the same serial number, but they would have a different governor's signature.
In questions and answers, the RBI released a statement that it is possible to have two or more banknotes with the same serial number. Still, they would either have a different inset letter or year of printing or signature of another RBI governor. An inset letter is an alphabet printed on the number panel of the banknote.
There are several types of fancy and unique numbered currency notes of India. Some twin notes have minor design changes or different years of printing.