PEBD: Pay Entry Base Date. This is the date that denotes how much of your service is creditable towards longevity for pay purposes. In other words, it is a calculated date based on creditable service. It can be found in field 4 of your last active duty Leave and Earnings Statement (LES). Your PEBD can be affected by broken service, lost time, transfer to/from reserve components, etc. (If you separated less than one year ago, your LES is available in myPay. Or, you can call the DFAS Customer Care Center at 888-332-7411 for one.)
DIEMS: Date of Initial Entry Military Service. This is the date a member first entered uniformed service in any capacity. This date is fixed—it does not change. Departing the military and rejoining does not affect DIEMS.
DIERF: Date of Initial Entry Reserve Forces. This is the date an individual affiliates or enlists in any Reserve component (Non-Extended Active Duty or EAD) for the first time. That date is fixed and is not adjusted for breaks in Reserve component service. That does not include time in the Active component Delayed Entry Program (DEP), the Reserve Officers’ Training Corps (ROTC), or the Professional Appointment Program.