Streamflow data derived from stage-discharge (HQRC) are reported without uncertainty compelling users to treat them as absolute and deterministic. However, ignoring uncertainty is no longer viable, as data users increasingly demand confidence in measurements - especially for cross-agency comparisons and scientific or legal scrutiny. This paper investigates a major factor affecting the accuracy of HQRC data: hysteresis caused by ubiquitous gradually varied flows (GVFs). Although hydrometric agencies apply costly corrections or use other methods to account for this effect, assessing their effectiveness is challenging and largely unknown. Consequently, most HQRC stations operate without accounting for hysteresis-induced error. Motivated by the lack of comparisons between data produced during GVFs by HQRC, HQRC corrections, and multi-variate monitoring methods, this paper evaluates the performance of several methods from each category applied to a range of flows at three gaging stations. Besides quantifying the HQRC uncertainty, we provide guidelines to properly account for it.