In recent years, performance management (PM) has become a buzzword in public sector organizations. Well-functioning PM systems rely on valid performance data, but critics point out that conflicting rationale or logic among professional staff in recording information can undermine the quality of the data. Based on a case study of social service staff members, the authors explore three recording logics. The findings reveal a complexity of recording behavior and show how frontline staff shift between recording logics according to the situation. The actual data recordings depend not only on the overall logic but also on factors such as attitudes, assumptions, and motives. The authors suggest that shifting recording logics weaken the validity of performance data. These shifts undermine the idea of PM as a trustworthy strategy to bridge the gap between professional and managerial staff, as well as the possibility of a well-informed management.