According to the document below, the "Last data copy" signifies the date/time when production data was last copied into your sandbox:"

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This is misleading because the date/time is updated even if the data copy is not completed successfully.

The date/time is updated to the start time of the data copy, even if the process fails at the export step, and no data is copied to the destination sandbox.

Ideally, this should only be updated if the data copy is successful.