I think the key parts are:
Start Date, End Date, Position such as 'It Project Manager/Scrum Master' and a brief description of the role and also the words 'Full Time basis'.
Two of the three references - (adding up to 10 years experience) that I sent were from companies that were no longer in business, so to help (not sure if it did) I printed off the company particulars from Companies House Register. One included the details of the director (at the time) who prepared my reference.
It must have been OK as the visa was approved quickly.