Hi Etienne,
Costing Status or Moved to History would be used to determine if an invoice or credit note has been processed by Day End.
The OE Order Header record does not store the AR batch numbers, so there is no connection to the AR invoice batch. It might be possible to do this if OE created Direct batches to AR, but certainly not if it created Retrieval batches. But it doesn't now.
From your questions, it seems you are looking for more than just IF an invoice has been processed by Day End, but also where it is in AR.
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Regards,
Softrak Tech Support