When the firm of Wilsford and Davis formed a partnership circa 1905 to produce watches, the watches they produced were largely sold to retail jewellers. Some watches had the retaler’s name on them. The watches were typically marked W & D on the cases, but no other markings were placed on the watches. It was about 1910 when Wilsdorf bought Davis out. It occurred to Wilsdorf that he needed to come up with a name for the new company that was unique, universal, and could be copyrighted. He named the company Rolex. For a time, the firm continued producing private label watches, but now the watches had the Rolex name on them. It could have been at about this time that the W & D initials were dropped in favour of the Rolex name (yours). The watch appears to me to be legit in every way.