The calendar base reads Wikidata: births and deaths of scientists, inventors, physicians, explorers and every Nobel laureate, discoveries and inventions, space launches, foundations, treaties and publications, each with its exact day, a description, the first paragraph of its Wikipedia article in English and in Spanish, and a free picture. Nothing is written from memory: every date is a statement of its source, and a date two sources agree on is marked verified. Importance follows how many Wikipedias cover the subject, so your agent asks for the big days with min_importance=2 and still finds a niche fact when it wants one.