"...When planning for retirement, one crucial step is to make sure you’re getting service credit for all your working time that counts toward your calculation. This includes not just credit for federal employment that obviously is creditable but also for certain types of employment that you otherwise might rule out or forget about—such as part-time or temporary work years ago while a student.
Creditable service applies to more types of employment than you might think. For example, it covers work such as service with the Peace Corps and Vista, volunteer service under the Economic Opportunity Act of 1964, employment as a United States Capitol Guide, and work as a substitute letter carrier..."
