Crystal plasticity models often employ a uniform initial dislocation density, typically set to representative values, as part of the constitutive description of plastic flow. In this work, we investigate the effect of spatially heterogeneous, slip-system-dependent initial dislocation density fields on grain-scale deformation heterogeneity and strain localization, while maintaining essentially indistinguishable macroscopic stress–strain responses. Although macroscopic behavior and global texture statistics remain similar, pronounced differences emerge at the local scale, particularly within regions of intense strain localization such as intragranular (micro-)shear bands. These differences are reflected in slip-system activity, strain localization patterns, dislocation density evolution, and localized lattice rotation within grains. The results demonstrate that uncertainty and variability in the assumed initial dislocation density primarily influence extreme local deformation responses rather than volume-averaged behavior, with important implications for the robustness of microstructure-informed predictions of localization-driven phenomena relevant to damage and formability.