It is not a great definition in my opinion. The sentence "as far as is possible and practicable" is too vague. It makes people claim that when it is merely very inconvenient to get a vegan meal, it is vegan to eat something with animal products.
In my opinion veganism should be the extention of human rights to animals. That would mean that even killing a pig for a heart valve to safe a human would not be vegan. After all, we wouldn't even kill one human to safe multiple others in a similar scenario because that would violate the rights of the to be killed individual. You could argue that it is better to safe more lives, sure. But it wouldn't be the 'pro-human rights' thing to do.
I believe that is more in line with the philosophy the vegan society was founded to promote than their own current definition.
It is in theory possible to obtain animal products without violating their rights. Like someone else mentioned, picking up a feather from the ground is totally vegan for example.
Wool however is a bit more complicated. The reason sheep produce massive amounts of wool in the first place is because we selectively bred them to do so. Shearing a sheep can be beneficial for the sheep, but it is a problem we should not have created (or continue to create) in the first place.
I think we should stop breeding animals that have all sorts of genetic problems we created. That includes sheep that don't shed and need shearing to not overheat in the summer, it includes chickens that lay so many eggs their bones break due to calcium deficiency, etc.