Top left: Distribution of the ratio of the periodicity (T) to the measured periodicity detected via the GLS method applied in the simulated light curves, including sine component and intrinsic AGN variability. Top right: GLS periodograms of five light curves randomly selected from the CSS V-band light curves, with time spans of 2236 days, 2475 days, 2217 days, 2208 days, and 2466 days (in orange, green, red, blue, and purple, respectively), similar to that of the ZTF g band. Bottom panels: Periodicity ratios between each subset with varying time steps (bottom left) and varying S/Ns (bottom right) and the original ZTF g-band light curve.