After each input or output statement that issues a checkpoint, the RETURN-CODE special register is updated with the return code from the checkpoint routine. Therefore, you can test whether the checkpoint was successful and decide whether conditions are right to allow a restart.
If the return code is greater than 4, an error has occurred in the checkpoint. Check the return code to prevent a restart that could cause incorrect output.
related references
z/OS DFSMS: Checkpoint/Restart (Return codes)