Difference maps (Planck TYPE 1 – xGNILC) for CO J = 1 → 0 (top), CO J = 2 → 1 (middle), and CO J = 3 → 2 (bottom) are shown in this figure. Differences are visible in the Galactic plane, but they are a small fraction of the total signal and lower than calibration uncertainties. For CO J = 3 → 2, the effect of the postprocessing of residual systematics shows up as a negative trough close to the Galactic plane and extended bright red regions above and below the Galactic ridge.