  G4NRF is a simulation module for modeling nuclear resonance fluorescence
(NRF) interactions in the Geant4 framework. In this work, we validate G4NRF
against both absolute and relative measurements of three NRF interactions near
2.2 MeV in $^{238}$U and $^{27}$Al using the transmission NRF data from the
experiments described in arXiv:1712.02904. Agreement between the absolute NRF
count rates observed in the data and predicted by extensive Geant4+G4NRF
modeling validate the combined Geant4+G4NRF to within $15$--$20\%$ in the
$^{238}$U NRF transitions and $8\%$ in $^{27}$Al, for an average $13\%$
discrepancy across the entire study. The difference between simulation and
experiment in relative NRF rates, as expressed as ratios of count rates in
various NRF lines, is found at the level of ${\lesssim}4\%$, and is
statistically identical to zero. Inverting the analysis, approximate values of
the absolute level widths and branching ratios for $^{238}$U and $^{27}$Al are
also obtained.
