The distribution of sources with discrepant fluxes at 12 and 25 µm greatly resembles the distribution of variable stars, suggesting that time variability is the dominant cause of such discrepant fluxes. At 60 and 100 µm, the distribution is much different, since the sources cluster in two patches in the Galactic plane for reasons that are, at this time, unknown. Only about 1,000 sources have discrepant fluxes at 60 and 100 µm. It is worth noting that the sources with discrepant fluxes are not predominantly found close to the ecliptic plane so that asteroids are not a significant cause of this problem (Section VII.F).
Roughly 50,000 sources are tagged with discrepant upper limits. These sources are mainly near the Galactic plane wherethe erratic behavior of the noise estimator causes this variation.