You really are forgetting that the Trust has to impress those who pay its way, which is the government.
If it can get the government to believe that there is the colossal number of 380 million people visiting its canals every year, then it will think it worth it.
I should imagine that most have an opinion of the members of the government, and one figure is just as good as another, so why not make it a 'round' 500 million, which will really impress and perhaps get more money.
Elaine Turner