If you find that `vagrant box list` somehow does not contain a box you previously had, you can sometimes add the box back if you still have the sources for it in `~/.vagrant.d/boxes`.

```
$ cd ~/.vagrant.d/boxes/precise64/0/virtualbox/
$ tar czf ~/precise64.box .
$ vagrant box add precise64 ~/precise64.box 
Downloading box from URL: file:/Users/ryanuber/precise64.box
Extracting box...te: 417M/s, Estimated time remaining: --:--:--)
Successfully added box 'precise64' with provider 'virtualbox'!
```

Probably better that you just re-download it if you can do that, but I'm on gogo inflight as I am typing this, so just re-downloading is not an option.