It all depends on whose site you're looking at.
If eg; your flights are DL ATL/AMS KL AMS/IST.
DL would most likely see as OPEN/ARPT Sometimes they see OPEN/O-KL
KL would most likely see as ARPT/OPEN Sometimes they see O-DL/OPEN

When an airline sees OPEN it means the coupon is in their control and has not been used.
From OPEN it will go to CHKN then to BRD and finally to FLWN.