Erm, I'm not sure if this has been said before, but I thought that a tape
in a state of 'empty' would remain that way until the re-use delay period
had passed after which time it would become a vault-retrieve or scratch
volume. That could be why your tape went from 'empty' to being used without
you seeing it.

I'm pretty new to all this though, so it's just me thinking aloud.

Thanks

Farren