Hi Shivam,
Are you sure that the example which you have given above is actual VBFA entries. If yes,then you should be able to find the link using the item relationship in VBFA (POSNV & POSNN.).
But you have said that when you check the document flow of the credit memo, you can see only one invoice. That is kind of contradicting your VBFA entries given above.
Most of the time we configure to create unique credit memos per invoice. So when you create the credit memo in VF01, you can enter multiple invoices. When you press save, you get the success message with the credit memo number which got created. But it does not mean that only one document got created. System show only the last credit memo number in the success message. So re check the VBFA entries for those invoices.
And FYI, it is totally fine to use the VBFA table to get the subsequent document relationships. But when you want to find the preceding documents, it is better to use those reference fields in the item table. VBRP-VGBEL/VGPOS in this case.