Those instructions aren’t meant for updates but for installing factory images, you could have just used the OTA update file without ever having to unlock your bootloader.
Never boot the system before locking it, that will reset get_unlock_ability and make it impossible to unlock it again if something goes wrong.
The official instructions are severly lacking and should have been updated long ago, if you follow them there is a good chance to brick the phone. I don’t think anyone touched those pages in almost a year.