Spherical power spectra after DD subtraction (top panel) and their difference (middle and bottom panels) for the simulated NCP dataset. The top panel shows Stokes IΔ²(k) after the DD subtraction step using the new (blue), old (orange), and point source (green) Cyg A model, and the thermal noise level (dashed grey line). The shaded areas represent the 1σ uncertainties. The middle panel shows the difference Δ_old² − Δ_new² (black dots), while the bottom panel shows the differences Δ_point² − Δ_new² (pink squares), and Δ_point² − Δ_old² (purple diamonds), with the associated 1σ uncertainties (values reported in Table D.1). The horizontal error bars indicate the k-bin extension. We added a small offset in k to the pink and purple markers in the bottom panel to avoid overlapping of error bars. The grey shaded area delimits the range in k where Δ² upper limits are usually extracted from LOFAR data, being the most sensitive range for LOFAR.