As per the NetVault Backup Administrator guide, you will have to scan such tape twice to import its indexes.
https://support.quest.com/technical-documents/netvault-backup/12.2/administration-guide/77#TOPIC-1096186
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When a tape is swapped between libraries, removed from the NetVault Backup Server, or loaded on a device that is controlled by a different NetVault Backup Server,
the NetVault Backup Server is unable to find any information about that tape in the NetVault database.
In this case, the first scan retrieves header information from the tape and adds this information to the NetVault database and then marks the tape as "foreign".
NetVault Backup cannot import backups stored on a “foreign” tape until you scan the tape again.
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