I'm curious to find out how a car judge decides whose the winner when theirs no 100 percent proof to say whats original or not. I've looked at a lot of engine bays and their are so many little details that are different. The owners of the concourse cars all claim their cars have been restored back to original so how does the judge prove otherwise.

I watched a couple of guys concourse judging an MG show a couple of years ago. It was kind of bizarre, two blokes dressed in white dust coats carrying clipboards, peering into the engine bays, pointing at hose clamps and writing down notes. They were judging heaps of different models, probably covering 40-50 years of MG. I can't see how the two guys could have been experts on all the different models that were being judged. I bet they were just basing it on whether the details looked about right, rather than loads of glaringly obvious modern stuff having been fitted.

Tim

Having been asked to judge at many events including "true" concourse events, its a thankless and unenviable task. As John points out a concourse car is very different from an original car, and many larger events make allowances for this, including a preservation class.
The truth of the matter is very seldom are there 2 cars that honestly battle for supremacy. In my experience the basics need to be followed before the details. Panel fit, paint, panel quality (most are full of ripples or wrongly restored panels). A car with genuine parts will always trump a car with replacement or remanufactured parts, despite differences in condition. Yes no one person can claim to know every modification and change and date of such done by the factory, but in reality it is seldom required to make a decision.
I know its upsetting when someone has just spent $60+k paying for their Mk1 Cooper S to be restored only to find they are beaten in a concourse (or even loosely guided show and shine, which often provides the judges with little scope for differentiation between details ). But as a judge it is sometimes difficult to bite your tongue and not to say " because your beautiful and shiny car is full of Chinese knock off crap, and your panel guy needs glasses.