Standard deviation of Λ and Q′ color excess measurements as a function of the peak optical depth of the 3 μm feature, derived from randomly sampling uncertainties in the photometric parameters and the extinction law. Solid lines represent Λ for different band combinations: Λ(K_S − W₁) in black, Λ(W₁ − I₁) in red, and Λ(W₁ − L′) in blue. Dashed lines show Q′ for the combinations Q′(K_S, W₁, I₁) (gray) and Q′(K_S, W₁, L′) (dark blue). The simulation demonstrates that Λ(W₁ − I₁) and Λ(W₁ − L′) maintain the lowest total uncertainties, even at high optical depths, due to the small wavelength separation between the bands.