Following failed upgrade from Lite 15.x to 16.3 Zorin incorrectly reports 16.3

General Help
1

Following failed upgrade from Lite 15.3 to 16.3 Zorin incorrectly reports 16.3. Consequently an upgrade is no longer possible. I have run:
sudo apt --fix-broken install
sudo dpkg --configure -a
sudo apt update
sudo apt full-upgrade
sudo apt clean

Despite this, when rebooting grub loads the 15.3 version image. I would be grateful for any help or advice.

2

Can you please clarify this?

Are you saying that at grub, it looks the same as 15? But upon reaching the desktop, the os-release states it is 16?
Or, are you saying that from grub through the desktop, it looks the same as 15, but os-release reports it erroneously as 16?