| Value | Category | 
                                    
                    
                        | 1 | Preliminary registration | 
                                    
                    
                        | 2 | 1st stage book of holding | 
                                    
                    
                        | 3 | 2nd stage book of holding | 
                                    
                    
                        | 4 | Other | 
                                    
                    
                        | 5 | None | 
                                    
                    
                        | 777 |  | 
                                    
                    
                        | 999 | Missing | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.