Doing that now may push some fluid out instead of letting air in, letting you know where the leak is. Whether its the brake line itself, or bleeder screw. If the only thing you did was flush the rear brake, what fittings did you all touch? I doubt you undid the brake line itself, but I bet you touched that bleeder screw(s). Im assuming your rear master has a bleeder screw as well as the caliper itself?
Edit: You flushed because you found you had no brake pressure. My suggestion is still legit to see where it may be leaking.
Can be done before and after. Before in the hopes of pushing some fluid out to show the user where the leak may be. After to confirm no more leaks.