OK, but why you have to make batches using [Work order No].[Line No].[Assemby No].[Batch No]?
You have:
-[Work order No] on 'Prod. Order No.' field on Output Journal
-[Line No] on 'Line No.' field on Output Journal
-[Batch No] on 'Journal Batch Name' field on Output Journal
You can join this three values in on new custom field if you have to have this information.
You can split quantites per some different dates based on same PO.
When you want to post, first make filter on desired date and than start posting procedure.
NAV will posting only filtering line. Rest will be remain for next posting.
Something like that...