Methinks this should be much like a PO and PO Line Items relationship. 1 RMA number with fields pertaining just to the RMA (e.g. CreateDate, CreatedBy, Status, etc.) and a related table for items returned under the RMA - one record per item. The RMA number should not be meaningful data. Generation of the number is a separate problem.
BTW, you cannot paste images in this forum so your attachment links don't work. See "how to attach files" at the top of the page.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.