It is a totally irrelevant argument if the user should have used automatic or specific receipt allocation four years ago for a credit note that is being issued today, Neither system allows for that invoice, which had been fully paid at that time, to be retrospectively adjusted by the current credit note.
Furthermore, the government procedures don’t require the user to actually “allocate” within their accounting system the credit note to a specific invoice, they just require that the user “declare” within the tax filing that the credit note has a relationship to a particular invoice. Read the wording on the form.
Yes. Within the credit note form the “Invoice” field is optional. If you want to allocate it to a specific invoice then use it, however, leaving it blank and using the “Description” field instead will provide the opportunity to have both the linking (noting) to an invoice and the adjustment available to the Accounts Receivable as a whole.