Watch for the journals below in the results you find in article database searches. They publish important peer-reviewed scholarship.
Four nuns sing from a liturgical book, with the choir mistress pointing out the words, Ämterbuch (Book of Offices), 1483, Germany.
Universitätsbibliothek Leipzig, Ms 1548, fol. 39v (Source: Universitätsbibliothek Leipzig, Public domain). More description in Feminae.
Usually researchers find more sources by looking at the footnotes in an article or book, but these will always be older than the publication you have in hand.
Citation indexes like the Web of Science (which includes sections for the Social Sciences, Arts and Humanities, and Science) are set up to search for sources cited in the footnotes of journal articles as soon as they become available.
This allows you to find newer articles which cite the books and articles you already know are key for your topic. By relying on connections between authors rather than subject words and by moving forward in time, citation searching can open up new avenues of research.
See this tutorial for more information on cited reference searching.