The lifecycle covered in an appraisal is defined by the scope of the CMMI model process areas selected for the appraisal. The lifecycle selected does not need to be covered by each representative project or work group; it can be covered collectively by the identified representative projects and work groups.
The CMMI Appraisal Method is based on the fundamental premise that to generalize about the extent to which best practices are implemented at the organizational level, a representative number of instantiations of the practice must be examined. For practices that relate to a project or work group activity (as opposed to an organizational activity such as engineering process groups), a representative sample of projects or work groups is identified as part of the appraisal planning and preparation phase.
Work with your Lead Appraiser to ensure you select the projects or work groups that make the most sense for your appraisal.