A sales return is for goods physically coming back, so it only applies to products. A credit note is for a money correction and applies to anything you billed, services as well as products. The same line can genuinely need both.
Until now, raising one reduced how much the other could still cover. It no longer does. Crediting a line does not reduce what you can still take back on it, and taking something back does not reduce what you can still credit.
One thing is still shared, on purpose. Stock can only go back on the shelf once, so if one receipt has already restocked a line, the other will not offer to do it again. Each screen also lists the other receipts raised against the same bill, so nobody raises a second one by mistake.