Rolex Submariner 168000
Rolex Submariner 168000 is a particular reference produced after 16800 and the main but not visible difference between the two watches is the use of a new stainless steel called 904L instead the 316L used so far.
In this reference, the caseback and the bracelet is still produced using the old 316L steel and the dial is only glossy. After the 168000, all the Rolex stainless steel production has gradually moved to the new 904L metal alloy.
Batch of production
From mid 1988 (serial number 9.*) to the end of production (through into 1989, serial number R*).
16800 or 168000?
In every Rolex Submariner 168000 the guarantee paper has still the 16800 code. Even the caseback has been engraved with 16800 reference. To know if a watch is 16800 or 168000, remove the bracelet and take a look to the code engraved between the lugs at 12 o'clock.
The reference engraved between the lugs could be modified to appear 168000 instead 16800. Here you can see an example of a correct engraving of 168000.