Only One Out of Five Archived Web Pages Existed as Presented

When a user retrieves a page from a web archive, the page is marked with the acquisition datetime of the root resource, which effectively asserts “this is how the page looked at a that datetime. ” However, embedded resources, such as images, are often archived at different datetimes than the main page. The presentation appears temporally coherent, but is composed from resources acquired over a wide range of datetimes. We examine the completeness and temporal coherence of composite archived resources (composite mementos) under two selection heuristics. The completeness and temporal co-herence achieved using a single archive was compared to the results achieved using multiple archives. We found that at most 38.7 % of composite mementos are both temporally coherent and that at most only 17.9 % (roughly 1 in 5) are temporally coherent and 100% complete. Using multiple archives increases mean completeness by 3.1–4.1 % but also reduces temporal coherence