Left: Distribution of the median spectral S/N within [12 047, 18 734] Å for visually identified quasars. The dashed red line at S/N = 2 marks an empirical threshold below which the number of successful identifications declines rapidly. Middle and right: Median S/N versus J_E and H_E magnitudes, respectively. Blue points show individual quasars, and the black lines indicate linear fits to log₁₀(S/N), with the fitted relations annotated. The dashed red line again marks S/N = 2, and its intersection with the fit defines empirical limiting magnitudes of J_E ≈ 21.5 and H_E ≈ 21.3, shown by dashed green lines. These values represent practical limits for reliable spectral identification of quasars in Q1.