It is nearly impossible to find a 16550 from the early 1984 production run. The watch remains unpolished but worn, with all its marks. The watch has a later production dial as the early Rail dials were spiderwebbing and replaced by Rolex in later services. The bracelet is with Solid End Links, dated 2005. 
 
Details:
 
Brand: Rolex
Model: Explorer II
Reference: 16550
Year: 1984 (8.47 Mill Serial)
Material: Stainless Steel
Dimensions:  40mm
Crystal:  Sapphire
Movement: Automatic 
Bracelet/Strap: 78790A SEL Bracelet Dated MA4 Clasp Code
Box/Papers: No/No