Is it possible to recover data on media with overwritten header? (4044478)

If a tape is marked for reuse, only the index entry is removed from the database. Only once the tape is actually written to does any data get overwritten. Media header being rewritten means that either a new backup actively reused the tape, or the tape was labelled manually.

Once something actually writes to the tape, the data is lost to the software - NetVault can only "scan" a tape as long as the original data is still on it and only the index entry has been removed from the database. The process of rewriting a tape involved rewinding it to the beginning and then writing new (header and other) data. By doing so, the logical end of media and end of data is reset.

From that point onwards, no software will be able to read data past this mark - the drive will refuse to position past this. So while the data might still partially be stored magnetically, logically it is lost to any software or regular drive.