We describe our methods to validate the absolute calibration of the infrared (IR) radiometry of the Midcourse Space Experiment (MSX) Point Source Catalog, version 1.2 (PSC1.2). These are based upon stars drawn from our current all-sky network of absolute calibrators and upon other stars that also support the calibration of ESA's Infrared Space Observatory and of several other satellites. Based on the mean ratios of (observed/predicted) irradiances for this ensemble of stars, all four of MSX's mid-IR bands are consistent with this network; i.e., there are no mean ratios that deviate more than 3 σ from unity. However, the two narrowest bands (near 4.3 μm) are significantly discrepant by a few percent. This paper probes the radiometry of stars fainter than those validated by an independent study of the primary and secondary MSX standards by Cohen et al. To provide the user of the PSC1.2 with a basis for comparison, we derive the IR properties of normal stars from measurements by MSX's IR focal planes.