Observed cosmic acceleration is not a physical expansion driven by dark energy, but a projection effect arising from irreversible internal structural differentiation within a closed universe. Structural Differentiation Cosmology (SDC) is a theoretical framework based on this idea.In SDC, the universe is treated as externally closed, with no inflow of energy, matter, or spacetime.Cosmic evolution is described not by the introduction of new physical entities, but by irreversible internal reconfiguration of relational structure. In version 1.4, the framework is brought into direct contact with observations.We focus on the growth-rate observable fσ8(z)f\sigma_8(z)fσ8(z), compare SDC predictions with DESI measurements and the standard ΛCDM model, analyze residuals, and highlight systematic deviations at high redshift.These features provide a clear and explicitly falsifiable distinction between projection-based acceleration and physical acceleration driven by dark energy.