The third pair of digits are definately known to refer to the year.
In this example the pickups were wound by operator #20 in the 23rd week of 1978.
Pickup Codes: OOWWYY Example: 202378 - It is believed the first two digits are an operator designation for the person operating the pickup winder, this according to Abigail Ybarra herself.The second pair of digits are the week, but I have seen one example where the second digits were 72.The trussrod was inserted through the back of the neck and the channel filled with the Walnut "skunk stripe".This manufacturing process was used regardless of whether it was a Maple or Rosewood fingerboard.Large Letter Stamps: Not 100% sure what these mean, but I have a theory they were used to grade a body prior to recieving a finish. I have seen four A stamps on Natural finished bodies, and a trans-red with an A stamp. I have also seen a D, along with an A on a Sunburst body.
This is just a theory, but if only A's were put on Natural finished guitars as an example, it could help determine if a guitar is refinished.
So, you can't afford that '54 Strat, or that '64, or even that '74 for that matter.
Your last chance to own a vintage Fender Stratocaster is with the guitars of the late 1970's.
ALOT of "1979" Strats with S9 serial numbers I've recently seen online appear to be from 1980, including the Strat I bought.
Body and Neck: All bodies are Ash, and usually a heavy piece.
In 1979 a notch was added for a ground wire lug in the control cavity and output jack cavity and a black shielding paint was sprayed into the cavities right over the lugs and wires that were soldered to them.