Astrometric motion of CCs present in both epochs. As the plot shows the difference in separation between the two epochs, a comoving source should be close to the origin (labeled by “2018”). A background source with null proper motion will move according to the dashed curve as a reflection of the target’s motion, ending in the blue circle labeled as ‘2021’ at the second epoch. The motion of CC0 (labeled by '0') and CC2 (labeled by ‘2’) is distinct from the cloud of background contaminants.