Professor Michael McMahon:

I will add something. Legislators often ask where they should look to find best practice. This is not the Netherlands, but most of the Scandinavian countries have detailed administrative data, which allow any authority or researcher to calculate with a degree of precision that would be a dream for us the number of people who, in their wills, leave X million euro of excess above some threshold and, therefore, that Y is the tax that could be raised. We use a back-of-the-envelope calculation, and it is an approximate, but there are countries that have administrative data that are carefully managed and linked.