Why are historical estimations so terrible?

[gagenater]

Causes of death are often very obscure. IIRC a thorough forensic review of causes of death for a random sampling of major US cities found that a good 20-30% of listed causes of death on certificates were arguable wrong, or at best speculative. When very old people die, or people people who already have known health issues it’s VERY common that only a cursory check for ‘causes of death’ is performed. When child and infant mortality was common, cause of death often wasn’t even investigated and it was simply written ‘failure to thrive’ or left blank because kids died so often for unknown reasons.

 

[Henry IX]

Censuses were often opposed by locals and local notables, being seen as a way of imposing a central tyranny and taxation. A good example of this was in the Kingdom of Burgundy, where the king destroyed the old Roman census documents as a gesture of reconciliation with his nobles, as it was seen as tool of royal oppression.

The only reason the Doomsday Book was compiled was that the local resistance had been crushed and William (and his heirs) had the loyalty of his nobles, at least in regards to optimising the exploitation of the locals. In virtually any other kingdom such an undertaking would have been impossible as it would have been opposed by the local nobility. A census represents a significant centralising of power as it removes the ability to raise taxation from the local nobility and gives it to the king.