He soon became so rich that he could lend money to the Duke of Wellington. In 1814, this son became the British government's secret banker for funding the Napoleonic wars. The family established a close network throughout Europe, with links to ship owners, transport companies and financers, among others. News spread very fast through this network.
Instead much of the data is estimated from surveys. This gives rise to measurement issues relating to coverage, sampling and non-response, but not such as to undermine their integrity. It is therefore normal to have revisions as new information that improves the accuracy of the data is received.