I saw these info on GT-R fun site written in Japanese. 
Early production model of BNR32s were assembled from August 21 1989 to August 1991 with chassis number 000051-017466. Then revised model had been produced from Augst 20 1991. Another revision was done in the begining of 1993.  
  
year/total number produced 
------------------ 
1989/4,555 
1990/8,426 
1991/7,081 
1992/7,961 
1993/6,204 
1994/7,465