As I'm sure you have read, this was a complicated fix with no documented outcome, successful or not. That's a shame considering how much effort Tony an the OP put into it.
Personally I would suggest that purchasing a "new" screen is the simplest solution. There are a number of situations where an external display (on a device intended to have a built in display) is just not going to work such as an OS failure or macOS upgrade.
If the cost of replacing the screen seems too much of an outlay then it's probably time to consider a new device.