This paper explores the unique challenges faced by newly regularized migrants who have experienced long-lasting illegalization. Adopting a life course perspective, it sheds light on distinct vulnerabilization processes they still experience (or do not experience anymore) related to legal status stratification.The empirical data consist of repeated, in-depth qualitative interviews conducted with individuals transitioning out of undocumented status during the implementation of the "Operation Papyrus" extraordinary regularization program in Geneva, Switzerland. The findings reveal that after regularization participants felt enormously relieved not to be deportable at any moment anymore; however, three key processes related to legal status stratification continued to make them feel vulnerable: 1) the lasting and potentially irreversible consequences of past illegalization; 2) the challenges of transitioning between legal statuses; and 3) the vulnerabilities stemming from newly obtained, conditional, short-term, and revocable residence permits. The findings also uncover mechanisms of reinforcement among these processes while these are also exacerbated by other co-occurring vulnerabilizing situations (such as the context of the COVID-19 pandemic).Understanding the complex mechanisms through which vulnerability is created and maintained over time helps to formulate recommendations for designing regularization programs that better mitigate vulnerability, while promoting social cohesion.