time assign column in media
when NetBackup goes to use a tape and mounts it, it gets assigned -
assigned means that NetBackup took a scratch tape with no assigned date and tried to use the tape today - does not mean that it wrote to it.
Now when NetBackup writes to the tape it gets an images ( this does not change the assigned date).
if the backup is good then the tape has an assigned date, and has a good images.
http://www.symantec.com/connect/blogs/understanding-how-nerbackup-writes-tape
Media gets time assigned when it is mounted on a drive for first time or when a good image has been written on a tape?
From my test, that as soon as the tape is mounted and written to, the assign time is set. It probably happens just prior to the actual write.
I wouldn't worry about it too much. It will be set at/around the time of the FIRST write to that tape