That's a good question, however there isn't an answer. There was 40, 046 serial numbers used from 48 to 52 for the model 77, this includes Row Crop, Standard & Industrial tractors. Beginning with 53 production the system changed, the serial numbers run in sequence regardless of model. Thus there is no way of knowing how many were built in 53 & 54, lets say they built 100 model 77 tractors then 100 model 88 tractors, in this instance the last 77 got a number and the next tractor built is a 88, it got the next number.
In addition serial numbers were used for other applications, like the transmissions in the 33, 35 & 40 combines have a Charles City S/N plate. Lull lifts and road roller also used S/N plates.