From what I'm reading ,the A ,B ,C on the heel of an old neck denotes nut width.Is this correct. Then explain all the different thicknesses of Jazz neck.Measured from the back to the fret board. The Geddy is much thinner than say a MIA Jazz. but both have a 1 1/2 nut. My old Jazz is thinner than the Geddy.Are all old Jazz's thin? When did they get thick.Did Fender randomly change the thickness of the neck. Thickness could or could not be special ordered? I'm really lost on this.