Why the date a lost ship leaves the navy list matters

Why do histories record when a sunk ship was struck from the navy list?

Because that marks when the navy stopped treating the missing ship as an available piece in its operational plans.

The sinking date records the physical event, while the striking date records a change in institutional knowledge. A ship that disappears may remain listed because its navy has not yet confirmed the loss. Until commanders conclude that it is gone, staffs may continue assigning it a place in strategic and tactical calculations. The administrative date therefore marks when force planning finally catches up with the physical event.