Professor Brainstorm

No connection to Covid at all, I am enquiring what the standards require in respect of a formal report sheet to be signed by the customer, as this is what I've always been used to but can't see where it clearly states that, and where I might need to argue the point

What is the requirement for a report sheet for corrective calls, for company and customer copies that are signed by the customer? Naturally it states in BS 9263 what should be recorded, but can this be, for example, a company internal paper/electronic form which the customer never sees and never gets to sign? For decades it's something that I've always had, a triplicate pad that the customer signs and receives their copy, but where does it state in which standard that it's a requirement?