The paper presents a new method for checking Unique and Complete State Coding, the crucial conditions in the synthesis of asynchronous control circuits from Signal Transition Graphs (STGs). The method detects state coding conflicts in an STG using its partial order semantics (unfolding prefix) and an integer programming technique. This leads to huge memory savings compared to methods based on reachability graphs, and also to significant speedups in many cases. In addition, the method produces execution paths leading to an encoding conflict. Finally, the approach is extended to checking the normalcy property of STGs, which is a necessary condition for their implementability using gates whose characteristic functions are monotonic.