Text encoding comes first. Accents, apostrophes, and non-Latin characters break queries, CSV exports, and PDF generators. Dates are next, especially when someone in Arizona books an appointment that crosses a daylight-saving change. Null and empty values slip into fields the code assumed were always filled. Then comes volume. A report that runs in half a second on 200 rows can time out at 2 million. And old records, created under rules that changed three years ago, trip new logic the moment a customer opens them.