The Education Insights Center produced a series of reports culminating in recommendations for the structure and governance of a preschool through higher education and into the workforce (known as a P20W data system). This brief follows up on that series, with a focus on data quality; the brief was informed by the author's experience using California's existing education and workforce data systems to conduct research, as well as conversations with 14 researchers and other experts who have significant experience using those data to conduct research, to develop data tools for educators and the public, and for operational purposes. [This report is an addendum to the series: California Education Policy, Student Data, and the Quest to Improve Student Progress.]