The IOTC Regional Observer Scheme (ROS) aims to collect verified data from observers onboard fishing vessels operating throughout the IOTC area. Since the scheme’s inception, the IOTC has developed and revised standardized reporting tools for CPCs to use when submitting observer data to the Secretariat. This paper aims to examine the evolution of the ROS reporting tools and evaluate the completeness of the observer data submitted by CPCs. Following recommendations from the Scientific Committee and CPCs, the tools have undergone four major revisions. The most recent version of reporting forms was released in 2025. Adoption of the official tools has been slow, and many CPCs continue to report using alternative formats. To examine the completeness of reported data, all observer data submitted through 2021 were compiled and assessed across three reporting levels: general, operational, and individual. For purse seine and longline fisheries, both database-integrated submissions and alternative-format reports were analysed. Observer data from both gear types mostly included general and operational data, but information on the individual level was less complete. No pole-and-line data have yet been incorporated into the ROS database, although alternative-format reports contain information across all three reporting levels. CPCs and the Secretariat continue to work on reporting of gillnet observer data. Overall, the reported data remain incomplete, suggesting that variation in reporting practices and the use of alternative formats continue to affect the consistency of information received The Secretariat continues to work with CPCs to strengthen reporting practices and support more consistent and comprehensive data submission.