There are various ways that you could use a second lower plate to expand your backup solution.
- You could use a copy of your lower plate as a 'backup of your backup'. If you would lose one lower plate, you still have the other one to recover your key. Remember that the top plate can be recovered, but the lower plate cannot.
- You could split the markings on the lower plate over 2 plates. This makes it possible to split your GRAPHENE backup in 3 parts that, each individually, give no information at all about your private key.