Thanks for the suggestions, Toby.
- This would be a great improvement. I think it would be a mistake to force a credit note to be derived from an invoice, but to allow this for easier/faster creation and to support a link back would be a great improvement.
- Yes, agreed, if the credit note was derived from the invoice, this would work really well. This would work well with Return Workflow Improvements too.
- There’s already a link both ways on allocated credit notes. Have you missed this or have I misunderstood what you’re asking for here? Please see below video
Cheers 
P.S. Don’t forget to vote for your own request, votes are very important 