We present the first systematic investigation of the differences among reference-quality ellipsometrically measured pseudodielectric function (epsilon) spectra of crystalline Si, which are nominally used to approximate the bulk dielectric function of this material. In addition to the expected influence of residual overlayers, we identify surface-local-field and energy-derivative effects, the latter representing shifts between bulk and measured critical point energies, as well as changes in excited-carrier lifetimes due to the surface. Model calculations indicate that these four effects account for nearly all differences among spectra studied, although a second-energy-derivative component appears at the E-1 transition in some cases. The isotropic contribution to the surface-local-field effect is observed for the first time.