arXiv:2608.10025v2 Announce Type: replace-cross Abstract: For safety-critical software, operational data (e.g. sequences of software successes and failures) can provide strong statistical support for reliability claims. However, insufficient detail about past software failures may leave assessments unable to account for important features of failure behavior. In this paper, we extend conservative Bayesian inference (CBI) techniques for reliability assessment to check the robustness of reliability claims based on such data. We show how insufficient detail in operational data can undermine software reliability claims in autonomous vehicle (AV) safety assessment scenarios: even when used conservatively, low-fidelity data may yield dangerously optimistic conclusions. While these findings are consistent with previous work on the impact of statistical model fidelity in Bayesian software reliability assessments, our work clarifies why attempts to use low-fidelity data conservatively can be naive. To the best of our knowledge, we give the first conservative estimates of the impact of data fidelity on reliability assessments.