Teacher learning in asynchronous online professional development (PD) is often measured by self-reported instruments, despite uncertainties regarding teachers' accuracy in their self-assessment of learning. This study explored whether teachers' self-reported "gains" in content knowledge for teaching aligned with those measured by direct assessments. Through quantitative analyses of data collected from 57 middle school mathematics teachers who participated in a fully asynchronous online PD program, we found no significant correlation between teachers' self-reported knowledge gains and those measured by direct assessments. Additionally, we examined the role of teachers' use of self-regulated learning (SRL) strategies, namely organization, elaboration, and monitoring, in their learning from the PD program by conducting linear regression analyses. Our results indicated that teachers who frequently monitored their understanding of the PD content demonstrated greater gains in their content knowledge as measured by direct assessments. However, none of the SRL strategies predicted the accuracy of teachers' self-assessments of knowledge gains from the asynchronous online PD program. These findings raise concerns about relying solely on self-reported instruments to capture teachers' learning in asynchronous online PD programs, and they emphasize the need for more robust and accurate outcome measures in the asynchronous online learning context.