Magnitude differences from three different photometric measurements for each source. Blue squares: difference in the large-aperture photometry of UVM2 and F225W; orange circles: difference in the GALFIT point-source magnitude of UVM2 and F225W; green triangles: difference in the GALFIT point-source magnitude of the F225W data and the GalSim-simulated UVM2 data. NGC7603 compares the F225W filter with UVOT/UVW1 instead of UVOT/UVM2, as no UVM2 data were available for this source in K. K. Gupta et al. (2024). For all but one source, the difference in the point-source magnitude between HST and Swift/UVOT data is larger than that in the large-aperture photometry.