How does a re-post IDOC knows that the SKU had been posted

Hi,

The WPUUMS had 5000 segments.

During the initial posting, some article documents and billing documents are created.

However, some SKU having problems and the IDOC status is set as "51".

When User re-post the same IDOC number in program, "RBDMANI2", how does the system knows whether it had already been posted or not?

Which tables or fields are there to denote that the SKU had been posted, and will not try again during the re-post?

Is there a special table that stores the initial posting results?

Thanks