Report Invoice group by origin

Hi all,

I have two deliveries with one text line and two item lines. I then copy these 2 deliveries to an invoice. In the invoice I can see:

text line delivery 1,

first item line delivery 1,

second item line delivery 1,

text line delivery 2,

first item line delivery 2,

second item line delivery 2.

I have created a report that groups the lines by Delivery but I don't know how to group the text lines correctly so that the text line is grouped with its corresponding delivery. The text lines (database table INV10) do not have a BaseDocument field so I don't see a way of knowing which delivery each text line originally came from..

How can I group the text lines with their corresponding delivery lines?