CTG = "Cartridge" in reference to the caliber of the gun not the model. The ".38 Special" cartridge is just one of a number of .38 caliber rounds and by far the most common. Some early models used the ".38 S&W" cartridge which is shorter and very slightly larger in diameter. If it says ".38 S&W Ctg." on the barrel without the "Special" it was chambered for that shorter round (which are still made but not real common).

There is a sticky somewhere on the forum with a listing of date ranges by serial number/prefix which should help get you in the ballpark.