Two datasets, each with 390,751 date samples from the UNT Libraries' digital collections. These samples were compiled for research regarding the Extended Date/Time Format (EDTF) standard. The first dataset contains a concatenated list of date values from the metadata records in The Portal to Texas History, the UNT Digital Library, and The Gateway to Oklahoma History. The "classified" dataset includes labels expressing whether each date is EDTF-valid and the level of conformance.