The capability to dynamically evolve process models over time and to migrate process instances to a modified model version are fundamental requirements for any process-aware information system. This has been recognized for a long time and different approaches for process schema evolution have emerged. Basically, the challenge is to correctly and efficiently migrate running instances to a modified process model. In addition, no process instance should be needlessly excluded from being migrated. While there has been significant research on correctness notions, existing approaches are still too restrictive regarding the set of migratable instances. This paper discusses fundamental requirements emerging in this context. We revisit the well-established compliance criterion for reasoning about the correct applicability of dynamic process changes, relax this criterion in different respects, and discuss the impact these relaxations have in practice. Furthermore, we investigate how to cope with...