Between May and October 2024, 82 potential interview partners were contacted via email. The first scientific interview (I-1) was conducted with a researcher who has professional experience in sustainability assurance, with the aim of calibrating the interview guideline and clarifying key concepts, particularly professional judgment. In I-11, both a partner and a sustainability auditor participated simultaneously. I-17 was not recorded at the participant’s request; its content is based on a contemporaneous memory protocol (MP) and detailed researcher notes. Seven interviewees had assured sustainability statements – Six from Big Four firms and One from the next-largest provider. The column “Interview Mode” shows the mode of each interview, with VC = Video Call, PH = Phone Call, and IP = In Person