Maps of systematic uncertainty in xGNILC data products arising from uncertainty in priors used for CO scaling parameters. The uncertainty in the CO J =1 → 0 and J = 2 → 1 maps are only in the region where we do a GLS, and so it does not contribute to any uncertainty in the Galactic plane. For the CO J = 3 → 2 map, the dominant systematics uncertainty comes from the postprocessing stage.