Comparison of our working sample of Galactic O-type stars (pink and black) to the complete list of stars of this type included in v4.1 of GOSC (gray). We separate in the two panels the stars for which we have been able to obtain spectroscopic parameters (pink) and those for which we did not perform any quantitative spectroscopic analysis. These last stars are not considered hereinafter (black). Left: histogram of stars with respect to the B-magnitude. The vertical dashed lines mark the 90 and 80% completeness limits in our sample using GOSC as reference. Right: number of stars per spectral type. Percentages indicate the respective completeness of stars marked in pink and black, in the bottom and top panels, respectively, with respect to GOSC.