In order to be compliant with statutory requirements in many countries, a rebate credit memo has to be treated like any other invoice.  Continuous number sequences, government approvals, taxes, and other regulations come into play.  There is also the need to produce a document to send to the customer or keep on file, like any other  credit memo.  D365 (and AX) instead put the rebate credit directly on the customer's AR account so there is no invoice number assigned and no chance to produce a printable/email-able output document.  This is not compliant with many localization standards and should be fixed.  It also makes AR management more difficult because the when the customer takes a deduction, they have no document number to reference to assist in matching things up.