An instant success since its launch, the ref. 16520 continues to achieve premium results at auction with an ever growing community of admirers and is considered as one of the most important sports watches ever produced. With that said, certain examples of the reference are certainly rarer than others due to distinctive traits that separates them from the rest. During the manufacturing process of the dial, one of the procedures is to apply a layer of varnish on the registers dubbed as Zapon. The nature of this varnish that was used in certain batches produced, developed a natural “tropical” brown hue over time at random. First realized in 2005 by acclaimed Italian auctioneer whilst putting together an auction that one example of the reference featured a much darker hue of the registers than the other. Despite the fact, the example with a darker register sold for much more. It is believed that examples bearing a S,N,T and W serial were common with such trait.