Can't register existing machines and disks in new VirtualBox installation

[nvivo]

I reinstalled my system from scratch and tried to register some existing virtual machines using VBoxManage.

I registered the base VDIs first, then tried to register a machine that had snapshots. I got the following error:

Could not find a registered hard disk with
UUID {31f4d85c-85d2-4e60-6da8-667d43a39d70}

I saw that this was an snapshot disk, so I tried to register that disk, then I got:

Hard disk image '/pathto/{31f4d85c-85d2-4e60-6da8-667d43a39d70}.vdi'
is a differencing image that is linked to a hard disk with UUID
{61bdd385-4f34-4e39-15be-c6029ea61724} and cannot be used directly
as a base hard disk

The solution was to copy my old VirtualBox.xml to the new home folder, but VBoxManage should register the disk as a snapshot disk if the parent disk is already registered, or even try to find the snapshot disks and register everything together.