Independent purity validation based on SDSS globular cluster Hertzsprung–Russell (H-R) diagrams. The six panels correspond to six globular clusters with good SDSS photometric coverage. Gray dots are all SDSS photometric point sources in the core region (r < r_t/3) of each cluster, forming the background stellar distribution on the (g − r, g) H-R diagram. All DESI MWS DR1 sources were cross-matched with these SDSS fields using a 3″ matching radius; the matched points are overlaid: green filled circles mark sources from the clean photometric BHB sample ﹩{{ \mathcal S }}_{c}﹩ that match the cluster field within 3″, and magenta open diamonds mark the matched sources from the clean spectroscopic BHB sample ﹩{{ \mathcal S }}_{{\rm{d}}}﹩. Blue crosses indicate matched noise (contaminant) sources, and triangles denote all other matched DESI non-BHB stars. The black boxes outline the typical BHB region (−0.3 ≤ g − r ≤ 0.0, with g-band magnitude within the cluster horizontal-branch range).