The information about restrictor sizes I posted earlier was wrong (http://www.rallycars.com/Cars/turbo_restrictors.html). Sorry for that.
1990: 40 mm
1992: Group A 38 mm and group N 36 mm
1995: Group A 34 mm and group N 32 mm
It was expected that the diameter would be reduced by 2 mm (1995) but FIA decided otherwise.
1995 was also the first year for kit cars.