In the fields of civil and structural engineering, online or real-time system identification techniques are experiencing significant advancements, particularly in developing emergency response systems and conducting autonomous damage assessments of infrastructures. From the standpoint of civil and structural engineering, online system identification can be utilized to monitor the modal parameters of structures, issue timely warnings regarding potential structural damage, and facilitate post-earthquake reconnaissance and rehabilitation efforts. To facilitate it, several techniques have been adapted into recursive formulations, and recently, subspace identification (SI) has been modified to create recursive subspace identification (RSI), which is capable of detecting time-varying dynamic characteristics of structural systems. This study introduces various recursive formulations for SI and provides a comprehensive discussion of the user-defined parameters employed in these techniques, examining the impact of these parameters on the identification results. To validate the proposed user-defined parameters in RSI, two distinct datasets are utilized: the first dataset comprises laboratory tests conducted on a specimen (multi-floor) with variations in column stiffness on the first floor, while the second dataset includes seismic responses obtained from a real building monitored by the Taiwan Strong Motion Instrumentation Program (TSMIP). In conclusion, this study provides a summary and general recommendations for selecting user-defined parameters in RSI, culminating in a comprehensive conclusion.