Start with the definition
A population, an application and an event are different things. One source may describe who lives somewhere on a given date; another may count movements over a year. Both can be useful without being directly comparable.
Make room for the period
The year in a report title and the period its data describes can differ. That is why our library presents the publication year alongside context for each external source.
Ask what is missing
A figure can be precise within its scope and still not answer the question we care about. Good source use also means clarity about what the material cannot tell us.