I can't remember half of the stuff I got taught when taking my driving lesson. Frankly a re test doesn't prove anything. Older drivers will just take lessons and go back to how they drove normally
Like all tests, it shows how good you are at faking/learning to drive properly, it doesn't show that you WILL drive that way.
Take a look at all the Taxi drivers who reverse into main roads, undertake, go over the speed limit by a great proportion, park pretty much anywhere to pick people up etc etc.