Hello Lorenz,
System will check if key_date is at or after open_date. If key_date is before open_date, then system will not execute accrual/deferral.
E.g. swap deal is created with Contract Date 04.07.2013 (open date), then the accrual/deferral can be executed with key date which is equal or greater than this date.
Hope this helps.
Best regards,
Jasmine