Every subject has an appropriate kind of evidence. A curated volcano database can identify a listed cone and its catalogue value. A peer-reviewed paper can support a result within its study period. A digitised contemporary letter can show what an observer or expedition recorded. None should be stretched beyond that role.
This reference keeps dates close to changing measurements. Glacier areas, isotope records and mapped outlines all depend on a method and observation window. Where credible sources differ, the difference should be described rather than silently averaged. Data and uncertainty gives examples.
Maps are sources too: their scale, survey, projection, edition and purpose determine what they can show. Historical maps illuminate past representations; they are not navigation products. Maps and geodata and Historical maps explain the distinction.
The site is a reference record: it concentrates on sources that can be read, dated and compared.