e0-dependent era weighting

Background: The structural scores (PCs 2-5) relax toward the canonical pattern at empirically measured rates, creating a visible regime shift in the derivative of the age pattern around the horizon where country-specific contributions fade.

Question / Future Work: Future work should investigate the possibility of implementing e0-dependent era weighting or employing adaptive kernels to smooth the transition when country-specific score relaxation yields to the canonical dynamics.