Record sources as you write, not months later when links may be lost. For each quotation, statistic or historical detail, save the author, title, publication date and page or URL. Distinguish a primary source from a summary and note when a claim needs expert review.
Check names, dates and permissions during revision, then provide your editor with the source log. This does not replace legal or specialist advice, but it makes review more transparent and efficient. Careful fact-checking supports reader trust and helps the finished book meet professional publishing standards.