For an individual covered under a nongroup certificate or under a certificate not covered under subsection (2), a health care corporation may exclude or limit coverage for a condition only if the exclusion or limitation relates to a condition for which medical advice, diagnosis, care, or treatment was recommended or received within 6 months before enrollment and the exclusion or limitation does not extend for more than 6 months after the effective date of the certificate. A health care corporation shall not exclude or limit coverage for a preexisting condition for an individual covered under a group certificate.