  We study the old problem of the uniqueness of chemical evolution models. We
showed in Molla et al. (1999) that multiphase models for three Virgo cluster
galaxies were able to reproduce the observed radial distributions of spectral
indices Mg2 and Fe52. But those models may fit the present-epoch radial
distributions with different star formation histories. The two spectral indices
are in turn affected by the well known age-metallicity degeneracy which
prevents the disentagling of age and metallicity for single stellar
populations. In this work we face both issues by analyzing a set of multiphase
models for the Virgo galaxy NGC 4303
