If the plan years are not the same, then there would be separate plans and would not be included in the same SPD. However, if the policy years are different from the plan year, then it is possible to be included. As an example, if a plan year runs from January to December (that is used for the 5500 filing), and the plan includes a medical policy that runs January to December, and a Dental policy that runs February to January, these can all be included in the same SPD.
Carriers will often refer to policy periods as “plan” years and use the terms interchangeably. However, the Plan Sponsor (ERISA), sets the Plan Year and it needn’t coincide with policy anniversary dates, nor must all policies renew simultaneously. However, for administrative purposes it is more convenient to have them all renew simultaneously.