Why can PNR status change before departure?

PNR status changes before departure because the railway booking system continuously updates based on cancellations, quota releases, and chart preparation. When a confirmed passenger cancels their ticket, the freed berth is offered to the next waitlisted passenger, which might be you. Vacant berths from unused quotas such as VIP, ladies, or foreign tourist quotas are also released into the general pool closer to departure. The final confirmation happens at chart preparation time about four hours before departure. After that the status is frozen and no further changes occur unless the railway makes operational adjustments.