Top panel: cumulative reliability for the union and intersection catalogues, as a function of dust contamination. Region 1 is the low-dust contamination region, being the 65% of the sky outside the Galactic dust mask, and region 2 is the complementary dustier region added to this when the smaller 15% dust mask is applied. The Gaussian noise limit is the expected reliability from purely Gaussian fluctuations. Bottom panel: histogram of the y-signal in a typical filtered patch from a null-test simulation, compared to the best-fit Gaussian (black dashed line). The distribution of y-noise is non-Gaussian.