This is a U series Daytona 16520
Case no. 16520/U610139
The Ivory dial was taken from my another very early production Daytona 16520 that has changed from white to Ivory.
U series is the most desired batch and with the ivory dial, it is unique and ivory dial Daytona has appeared in major auction house auction couple of times over the so many years.
A watch dial changes color due to moisture and heat due to carelessness of owner not tightening the winding crown or some rubber parts have worn out.