Rolex case serial numbers are stamped during an allocation run of that particular model....... it is a myth that numbers actually correspond to a particular year...... They only give an approximation based on WIS reports around the world of what they have seen, or think that they know.. The fact is, Rolex is like any business.. they only make a run when they have enough orders to fulfill; so they may make a few thousand Z models in 2006, run off a few thousand more in 2007, introduce a new prefix - get an allocation of proposed serials with that prefix - then in 2008, perhaps make a few thousand of each, and so on...
It is physically impossible to make and stamp all cases within a few months like many perceive for each prefix, then store all these parts in the back room.
For movements:
They have their own serial numbers and, like cases, are put together at some point in time, then sent for a COSC cert. Upon receiving them back, they go into inventory until a particular model run is in demand in the marketplace (see above)..
At that point, a case and a movement, each with their own individual serials, are married up and the "as built" records are prepared.
Rolex has many more models than they do movements. For example, any 3186 can go in any GMT II or Exp II. or any 3135 movement can go in any Sub, YM, DSSD, DJ and so on..........