Correlation between the shape of the metallicity gradient over time and the range in [Fe/H] measured across age bins using the method with (solid lines) and without (dashed lines) our proposed correction applied for our sample of 178 TNG50 MW/M31-like galaxies. The colored lines correspond to the correlation of galaxies with different bar strengths, with the black line providing the density of the entire sample. A correlation of −1 implies that the shape of the gradient can be perfectly recovered from Range[Fe/H](age), and that the method is successful. With no correction applied, the median correlation is −0.74 (median absolute percent error of 28%), whereas when applying the correction the median correlation improves to −0.88 (median absolute percent error of 20%). The correction has a smaller improvement on stronger-barred galaxies (yellow) where the method already exhibited good success, but the correlation of galaxies with weaker present day bars show an improvement of over 40%.