Sales Order not generates Invoice or Credit memo at Receivables.

Hi,
I had a issue where Sales Order stuck at Interface level. This issue occurred due to SO date in closed period and it's resolved once SO date changed to latest open period at Interface level.
But in the business scenario several Sales Orders got delayed to several issues.
Why sales order generate Invoice or Credit memo for Sales Order in the same month.
What are the possibility to generate AR invoice or Credit memo for Sales Order even though it's date in closed accounting period.

Please suggest.

Thanks,
Krishna