What the figures are built from, what is newly available, and how much the numbers move when they are revised.
Every series the site tracks has changed its own history at least once. Excess-mortality estimates for 2020 and 2021 moved by a quarter or more when the ONS changed method in 2024. They differed by a factor of two or more between agencies, depending on the baseline chosen, whether ages were standardised, and how the pre-pandemic trend was extended. Census results in 2021 and 2022 rebased population estimates and every rate calculated from them, in some countries by several per cent. Late registrations lift recent death counts for months. A shift in a cause's share can be a change in coding as readily as a change in deaths, as certification practice differs between countries and automated coding arrived at different times. None of this is error in the ordinary sense. It is how statistics improve. That said, the size of a revision is rarely reported alongside the figure, and conclusions drawn from one vintage do not always survive the next.
Registers open to researchers and close again. Statistical offices change what a series covers, how long it takes to appear, and who may use it. Series stop. Each of those changes what can be known and when, and none of it is reported as a finding: it appears as a note on a release page, if at all. This page collects them, alongside the mechanics that decide what a figure means in the first place: how a death is certified and coded, when it is registered, which population sits in the denominator, and how a rate is standardised before anyone compares it with another.
