Sales
Quotation to order to fulfilment to invoice, priced from the customer’s own list and checked against a credit limit that counts what has not been invoiced yet.
What was quoted is what gets billed
An order carries forward the quotation it came from, and the invoice carries forward the order, so three documents written by three people cannot quietly disagree.
Credit counts three terms, not one
Outstanding receivables, plus confirmed but unbilled order value, against the limit — a limit measured on invoices alone is satisfied by never invoicing.
A return is a document, a credit note is a separate one
Goods can come back for replacement with no money moving, and a price can be credited with no goods involved. Forcing one to imply the other is the wrong answer for both.
Where the goods go is not who owes for them
A delivery can be addressed to the customer’s own client without changing who is billed or what their terms are.