Implicit effective date on changes only HCM Extract

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We have a changes only HCM Extract that isn't passed an effective date for the scheduled run. We are seeing some issue where people aren't coming through on the file. 

People in my organization think it is related to the sequence of the assignment changes, but i'm beginning to wonder if it is related to the effective date of the assignment row we are trying to pull.

If there is no effective date passed on the scheduled run, is there some implicit effective date (like SYSDATE) or something like that that gets used? Or will it actually pull every change regardless of the effective date?