If you use SFLNXTCHG it means that every record in the subfile is marked as changed, whether you have changed it or not. Therefore your READC will read every record in the subfile. If you don’t use SFLNXTCHG then READC will only read the records that you change.
Sflnxtchg can work like you probably want it to, setting some records so the next cycle of READC will find them.
1. SFLNXTCHG must have an indicator associated with it. If it doesn’t have an indicator all records will be used by readc every cycle.
2. When you readc or chain a sfl record and want a SFL record to be availabe for the next cycle of READC set the indicator so that SFLNXTCHG is in effect and then update the record. Otherwise when you write or update the SFL record make sure you have the indicator set of SFLNXTCHG is not in effect.