Selection probability of the GCNS sources with RUWEs larger than our threshold shown in Fig. 3 across the colour–magnitude diagram. For the MS and WD sequence, we see a gradient on the selection probability for bins at the same G_BP − G_RP colour. The region between the MS and the WD sequence, which contains the MS–WD binaries, has a high concentration of sources marked as having poor astrometric solutions in the GCNS.