Appears there are four different udev disk directories not three.
/dev/disk/by-id
/dev/disk/by-label
/dev/disk/by-path
/dev/disk/by-uuid
If you have only virtio disk (/dev/vda) then you will not have /dev/disk/by-id
If you have only virtio disk (/dev/vda) plus a disk label you will have /dev/disk/by-label and that is good enough for grub-pc wrt. installing/updating.
Appears there are four different udev disk directories not three.
/dev/disk/by-id
/dev/disk/by-label
/dev/disk/by-path
/dev/disk/by-uuid
If you have only virtio disk (/dev/vda) then you will not have /dev/disk/by-id
If you have only virtio disk (/dev/vda) plus a disk label you will have /dev/disk/by-label and that is good enough for grub-pc wrt. installing/ updating.