I've noticed the same thing that books on MB's sometimes say 1991, yet others list it as 1992, but the reality is that 1st gear start cars were 1992 models that were released for sale in September of 1991.
So it was 1991 that you could buy one, but they were 1992 model year cars.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".