A post-production characterization approach based on spectral photometric and ellipsometric data related to a specially prepared set of samples is proposed. Single-layer (SL) and multilayer (ML) sets of samples presenting building blocks of the final sample were measured ex-situ, and reliable thicknesses and refractive indices of the final ML were determined. Different characterization strategies based on ex-situ measurements of the final ML sample were tried, reliability of their results was compared, and the best characterization approach for practical use, when preparation of the mentioned set of samples would be a luxury, is proposed.