US # 912b used Luxembourg REVERSE PRINTING error, which on this stamp issue means that the color portion was printed after the black stamp lines in reverse order of how they were intended to be printed. This stamp clearly exhibits all the identifying characteristics that I have circled in yellow in the pictures. You will notice how the black flag lines diminish because of having the color printed last and covering over them. This is more notable on the lines covered with the red ink, but evident also with the blue ink. This stamp has excellent centering, superb color, great perfs, solid paper without any tears, cuts or thins, and has a clean CDS cancel.