Can a person receive creditable coverage and still be a participant in the plan. For example, John and Mary are married and Mary has participated in John's employer's plan for 2 years. Mary gets a job and the questions is: Does the 2 years of coverage under John's employer's plan count towards the pre-existing condition limitation in Mary's employer's plan even though Mary continues to be covered under John's employer's plan?

Does the following excerpt from PWBA answers your question?

A group health plan is required to allow special enrollment for certain individuals to enroll in the plan without having to wait until the plan's next regular enrollment season.

A special enrollment opportunity occurs if an individual with other health insurance loses that coverage.

A special enrollment opportunity also occurs if a person has (or becomes) a new dependent through marriage, birth, adoption or placement for adoption. However, you must notify the plan of your request for
special enrollment within 30 days after losing your other coverage or within 30 days of having (or becoming) a new dependent.

If you enroll as a special enrollee, you may not be treated as a late enrollee for purposes of any pre-existing condition exclusion period. Therefore, the maximum preexisting condition exclusion period that
may be applied is 12 months, reduced by your creditable coverage (rather than 18 months, reduced by creditable coverage).

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I don't why her prior coverage wouldn't reduce the pre-x exclusion period. If she continues to be covered by her husband's plan, they do not have to automatically send her a certificate because she has not lost coverage. However, if you look at the definition of creditable coverage in HIPAA and the regs, there is no requirement that the other coverage be terminated before it qualifies as creditable coverage that reduces an exclusion period. The second plan will need to get on the phone to the first plan to confirm her continuous coverage, or accept other types of proof from the woman.