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Something happened for my friend: on a saturday after work at shanghai, I am going home with my coworker (who was travelin on a ID100 ticket) and got denied at check in, he then go to wait list counter for a sequence number. The number is a the earlier the lower basis.
When the previous flight closed for check-in same happened as other OP mention: DMP - DM - GO - OW EM - rest in sequential number. My friend didn't get though then he called his wife. I think his wife put him in some sort of priority and got cleared from HK for next flight out.