CuDiDi distribution of the photon-arrival-time asymmetry, showing μ_lower vs. μ_upper for all sources we analysed (background-density map). The diagonal black line indicates the locus of temporally symmetric light curves, μ_upper = μ_lower + 0.5. The green lines mark the empirical persistent band, defined as |μ_upper − (μ_lower + 0.5)| ≤ 0.2. Sources within and below this band are considered non-transient, while sources above are classified as transients. The 765 transient candidates in our golden sample are overplotted as light blue points. By construction they lie above the band, but their spread within this region reflects a wide range of asymmetry strengths. The bulk of the overall population clusters around (0.25, 0.75), as expected for approximately constant emission.