Rolex Gift

[hchavarria]

I just recently received a Rolex Submariner two-tone 16613 as a gift and was trying to determin the authenticity. I have the sales receipt so I know it has an authentic like price tag but my serial starts with an S and from my online research I noticed that I only see the 16613 mentioned as F and M series. This watch was purchased in 2005 and was handed over to me after a family member's death but they did not have the authenticity certificate or box.

I also noticed online that the strap buckle is two-tone but this strap buckle is only steel, the engraving on the buckle has a T4 marking suggesting it was built in April of 2005 but the S serial suggests 2003 built date. Any other ideas on how I can determine its authenticity?