The routing for SQ21/22 tends to change daily. The goal is to have a minimum time track. So, as the winds change the route will change also. The original plan was to use the polar tracks, however, the LAX
flights have demonstrated there are quicker routes.
Most likely in the winter, you will see most of the EWR
flights use a more polar route. However, you will also see more direct easterly routings to take advantage of the favourable winds.