Top panel: 2MASS image with the two background stars that Luyten 143-23 passes by in July 2018 (green circle) and in March 2021 (white circle), respectively. Bottom panel: Pan-STARRS image with the background star which Ross 322 passes by in August 2018 (green circle). The exact positions of the background sources are indicated with small dots at the centres of the circles. Their motions and the uncertainties are smaller than the size of the dots. The triangles indicate the J2015.5 positions of the lens stars measured by Gaia. The predicted motions are shown as thick blue/thin red curves, where the thin red parts indicate the epochs at which the stars cannot be observed. In both panels, the original positions (at earlier epochs) of the lens stars in the 2MASS and PanSTARRS images are indicated as squares. Larger views of the sky areas are displayed in the insets. The blue lines in the insets show the motion of the lens stars until 2035.