Read document flow at the time of Partner determination

Creating a followup opportunity on top of an existing opportunity. During this, Sales manager and Employee responsible needs to be copied from Old opportunity to new.

For this due to some constraint, i need to write a code in Partner determination procedure BADI(COM_PARTNER_BADI~DETERMINATION_ADD_IN_1) to find the old opportunity partners.

Here the issue is unable to read the document flow in the Partner determination procedure BADI.

My question is, is the document flow link is established after the Partner determination ? if yes then how can i read doc flow (Old opportunity-> New Opportunity).

If docflow is created well before Partner determination, then why i CRM_ORDER_READ_OW / OB are failing to get the document flow.

Thanks in advance for your expertise.