Estimates of potential output and the output gap are crucial for policy analysis but are unobservable and uncertain in real-time. This paper investigates revisions to these estimates made by the European Commission, Eurosystem, IMF, and OECD for the euro area and its member countries. It analyzes forecast vintages from 2002 to 2025, comparing institutional reliability and breaking down output gap revision causes. The study finds significant institutional differences, with the European Commission showing the least revision and the OECD the most in a balanced sample. Eurosystem estimates have notably stabilized over the last ten years. Revisions to the output gap are primarily influenced by changes in real GDP data and potential growth figures. Errors in nowcasting have a less substantial impact on these revisions. Panel regressions demonstrate a significant link between real GDP data revisions and medium-term forecast errors with potential growth revisions. This suggests that initial estimates of potential growth are adjusted to reflect revised or unforeseen GDP developments. The findings underscore the inherent uncertainty in real-time output gap assessments. Consequently, the research advocates for the use of supplementary indicators to gauge economic slack.