No, it is not necessary for the dates to coincide. Your plan can be set up to begin any month; the 12 month period will not be affected by the 15 month renewal by the insurer. If a Form 5500 is filed, the insurer will proved Schedule A premium information for the plan year being filed. Information on the Schedule A is a maximum of a 12-month period. However for purposes of creating the plan, the employer selects the year and it need not be changed if a policy year changes. A plan can have multiple policy years without having an effect on the actual plan year.