Evaluate the specific statutory criteria required for diverse candidates to successfully acquire Indian citizenship:
1. A Person of Indian Origin (PIO) is legally entitled to apply for registration after maintaining ordinary residency in the country for a period of five years.
2. An individual legally married to an Indian citizen automatically qualifies for citizenship regardless of their physical residency status within India.
3. A PIO who migrated into Assam from Bangladesh prior to January 1, 1966, qualifies under a specialized historical provision.