Whilst not a PIP example, i’ll just tell you about my wife’s transition from Incapacity Benefit to ESA.
She was given no points whatsoever following her face to face assessment, despite having problems since birth which have steadily got worse through life leading to a cocktail of health problems, and being ill health retired at the age of just 33.
We took it to appeal tribunal and they put her into the Work Related Activity Group, I kept fighting and she ended up in the Support Group. That was 2012 and she’s still at that level now.
A real example of it being possible to go from the worst outcome to best outcome possible.
So that shows how wrong they can get it.
Its always worth fighting if you believe its wrong and can assemble sufficient supporting information to evidence your case.
Remember DWP have an interest in minimising your claim. The Tribunal Service has no axe to grind whatsoever, and if you can capably articulate and evidence your claim there’s a good chance you can pull off an improvement.