Hello,
1. A successful backup job only confirms that data was written to the tape; it does not verify that the tape can be read or restored from the media which a verify option on a job does.
2. If a job is cancelled, the backup of the files does not complete so the job cannot be held as good. If it fails during verification, even then it suggestes some problem with the files backed up or the media or any such factors, so can't be held as good either.
3. Verify process is always recommended. In order to better understand as to how it works and what it does, refer to the following technote:
How do the "verify" and "write checksums to media" processes work and why are they necessary?
http://support.veritas.com/docs/245177
Hope that answers your question. In case of further doubts, revert to the forum with details.
Note : If we do not receive your reply within two business days, this post would be marked ‘assumed answered’ and would be moved to ‘answered questions’ pool.
Regards.