Confocal Raman optical sectioning is a most frequently used technique to obtain non-destructively clear images deep within a thick sample; however, this technique has been known to have the problem that the sample-induced spherical aberration degrades the quality of the images not only laterally but also axially. Here we hence consider the applicability of digital super-resolution reconstruction to this technique. Before the reconstruction we numerically analyzed so-called the "confocal volume" within a sample. The numerical analysis revealed that, with probing deeper inside the sample, efficiently-collected in-focus regions decay due to sample-induced spherical aberration. It is also found that the aberration volume is responsible for the difficulty in the quantitative interpretation of depth analysis.