Can a castrated board still have boar taint?

That is not likely. The risk thereof is virtually zero.

Can everyone smell boar taint?

Not all people are equally sensitive to the substances androstenone, skatole and indole that cause boar taint. Some people do not smell androstenone; others think it smells nice and a third person may indeed find that it is different in the fragrance. In general women smell it better than men.

How is prevented that meat with boar taint reaches the consumer?

Slaughterhouses that process uncastrated pigs (boars) have the responsibility to ensure a reliable detection method. A good (with figures substantiated) and available method is the HNS system. For this purpose, during the slaughter process some fat of the pig is scorched and a trained inspector checks the smell. This is called the HNS system (Human Nose System). Pork that smells different is kept separate and used for products where the meat is not heated.

Is meat with boar taint destroyed?

No, there is absolutely no reason to. The meat is of excellent quality for making, for example, boiled meat products or dried sausage. Consumers can only notice boar taint if they heat the meat.

What percentage of pigs has different boar taint?

Research in large slaughterhouses in the Netherlands, Germany, France and Belgium shows an average from 3-5%. It varies even from farmer to farmer. With further tightening of farm management (hygiene, genetics, feeding, housing) this probably can be reduced even more.

There is a difference between research figures for boar taint in Denmark and other European countries. Why is that?

This difference arises because of the existence of different parameters. In the Netherlands the average is about 3-4%. This concerns the so-called hedonic parameter for boar taint, i.e. as experts perceive it. The 10% in Denmark stands for the percentage of animals having a level of skatole and / or androstenone which is above pre-specified limit values.
For skatole the limit is >0.25ppm. At higher levels of skatole and androstenone, the chance of boar taint increases. It may be that human experts smell boar taint at 3-4% of the carcasses, while 10% of those carcasses exceed 0.25ppm.
When Danish or German experiments refer to boar taint, it generally concerns the levels of skatole (and sometimes androstenone). This is not the same as the percentage of boar taint that is perceived by humans.