- Create SO101 and attach doc A
- Generate a sales invoice from SO101 and doc A is attached to the sales invoice
- Add doc B to SO101 (so now there are 2 attachments)
- Generate another sales invoice from SO101 and have doc A and doc B both show up as attachments on the new sales invoice
- Repeat as many times as needed, with each new sales invoice generated having all existing attachments come through