IUCN criteria are the most authoritative and objective to assess the conservation status of animal species. Although IUCN criteria are purely descriptive in nature, they can be interpreted as e.g. the relative size of the annual population growth factor (λ, the dominant eigenvalue of a projection matrix). This enables quantitative assessment based on demographic data (survival and reproduction). However, such an assessment for many species is hampered since demographic data are often incomplete. To facilitate assessment when demographic data are incomplete we extended an existing framework (developed for species with a pre-adult stage of one year) to apply to species with pre-adult stages (=juvenile and sub-adult together) longer than one year. We develop both Leslie-matrices and stage-structured matrices and compare these with respect to eigenvalues, and both sensitivity and elasticity of underlying parameters. We illustrate our work with life history data and conservation status of a few marine mammal species.