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 first three digits refer to the manufacturer, CTS.
The last four are broken up into pairs, where the first two, 78, stand for 1978 and the last two stand for the week, which is the 18th.
They are believed to just be some kind of quality check stamps.
Pot Codes: MMMYYWW Example: 1377818 - In 1977 found on the side of the pots, moved to the bottom (and unfortunately sometimes covered with solder) in 1978.
A linear taper pot changes resistance evenly; at about half rotation (12 o'clock) you'll get roughly half the total resistance of the pot. Looking down at the top of the pot with the solder lugs facing away from you, put your two meter probes on the left-most and center solder lug.
Neck Configuration Codes: 00 = Rosewood fingerboard 01 = Rosewood fingerboard 02 = Maple fingerboard 03 = Maple fingerboard Neck & Body Stamps: WWYD Example: 0304 - Basically the same as the date portion of the nine digit neck stamp although in black ink.
They seem to be found on the bottom of the neck heel, as well as in the neck pocket of the body, or even just stamped on the front under the pickguard on Natural finished guitars.
If you turn this linear taper pot up about three quarters rotation you'll measure 20-25% of the total resistance value.
When you turn the pot up all the way clockwise you will probably still measure some resistance, say 2 to 60 or so ohms. You find that the resistance changes only 15-20% or so at half rotation, reading half the total resistance value only after you've reached almost three quarters rotation and then it drops rapidly (logarithmically...). Essential parts for guitar and amplifier restoration; fits the pots and jacks found on those great '50s to the present day USA guitars and amps.
Some might go by the pot codes, but those could have been stock a year or more old by the time they were put into the newly finished guitar.