Final answer:
Official Military Personnel files are normally updated after events like promotions, not during annual holidays, birthdays, or retirement.
Step-by-step explanation:
Official Military Personnel files are typically updated after significant career events such as promotions, reductions, transfers, casualties, and similar occurrences during a service member's active duty. Among the choices given, the correct event after which Official Military Personnel files are usually updated is C. Promotions. The updates will include the authority for the promotion and other pertinent details, ensuring the Personnel files accurately reflect the service member's current status.