Overseas Citizen of India (OCI) Card: Who is eligible to apply and who is not?

According to the OCI portal:
Any person of full age and capacity: –
(i) who is a citizen of another country, but was a citizen of India at the time of, or at any time after the commencement of the Constitution, i.e. 26.01.1950; or
(ii) who is a citizen of another country, but was eligible to become a citizen of India at the time of the commencement of the Constitution, i.e. on 26.01.1950; or
(iii) who is a citizen of another country, but belonged to a territory that became part of India after 15.08.1947; or
(iv) who is a child or a grandchild, or a great-grandchild of such a citizen; can register for an OCI card.

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