A bit of history...
Beetle (air-cooled) from 1946 = Type 1 plus derivatives Karman Ghia etc. all type 1 range
Transporter from 1950 to 1967 = Type 2 many derivatives Ambulance, Fire tender, Camper etc.
Transporter from 1968 'Bay Window' introduced originally designated Type 2/68 but soon dropped and continues as Type 2 until 1979.
1600cc saloon (notch back or square back) fast back and variant (estate) = Type 3 (1961 - 1974) - Karman Ghia derivative still within Type 3 range.
1700cc (later 1800cc) saloon or estate 1968 - 1974 = Type 4
Transporter 1980 - 1990? originally known as a Type 25. Air-cooled petrol until 1982 then water-cooled petrol. Diesel VW Golf derivative engine becomes an alternative early in 1980s. Syncro 4WD also available.
Note that I have used the description 'Type' NOT 'T'
Transporter T4 introduced in 1990 complete redesign with petrol or diesel engine in the front and front wheel drive or Syncro 4WD
Transporter T5 introduced in 2003
Transporter T6 introduced in 2016
Now this is where the confusion comes in, soon after the introduction of the T4 VW began to call the Transporter range as below...
Transporter 1950 - 1967 became known as a T1
Transporter 1968 - 1979 became known as a T2
Transporter 1980 - 1990 became known as a T3
Transporters from 1990 as we know them T4, T5 & T6
Confused? You may be as the above just scratches the surface of VW model designations and that's without going into those manufactured in Brazil, South African, etc.
Rod