I also agree that any time invested is a consideration of experience. However, the design of a letter is the decision of the employer, not the employee. Many companies assess the working staff annually; unfortunately, this situation may not be the norm, but it does occur. I have been in situations where, for personal reasons, an employee needs a letter of sorts—legal, insurance, credit. If an employer feels as though the employee simply does not have sufficient time to determine value, then a simple letter of employment may suffice. For example, employment date, title, job responsibility, validation of area or work assignment, shift assigned, punctuality. The bottom line is to discuss this request with HR; proceed with policy, and if no policy covers the topic, then confer with HR for the legal design, and the supervisor can supply the content.