Product line models (PLM) are important artifacts in product line engineering. Due to their size and complexity, it is difficult to detect defects in PLMs. The challenge is however important: any error in a PLM will inevitably impact configuration, generating issues such as incorrect product models, inconsistent architectures, poor reuse, difficulty to customize products, etc. Surveys on feature-based PLM verification approaches show that there are many verification criteria, that these criteria are defined in different ways, and that different ways of working are proposed to look for defect. The goal of this paper is to systematize PLM verification. Based on our literature review, we propose a list of 23 verification criteria that we think cover those available in the literature.