media (not) appendable (until)

Hi,

Lately my backup job failed a few times. I began to check the tape properties. Now I saw that for some tapes there was a date set on appendable until... (these dates are all ending this month), some tapes have the property 'not appendable' and one tape even had 'not appendable' (end marker unreadable).

Where can I change these settings? And which setting is preferable?

Thanks a lot,

Sofie