I'd guess possibly Nissan don't even know what number yours was out of the 500, assuming there were 500 made as they don't have plaques on like some limited edition cars and weren't built sequentially ie 500 in a row. Like I say, it's just another random RB out of many. Mine is definately one of the early ones as it's in the 0006xxs.
For Nissan to even think about competing in the rallying they had to build 5000 cars between 01/01/1991 - 31/12/1991 and before the end of 1991 10% had to be Homogolated ( RB ) as a minimum for them to compete.
As the RB came with extras such as more expensive differentials im sure they would have budgeted just for 500 why any more??, (im guessing)
as my chassis number is around 00576* im assuming they built around 600 cars in 1990, and 5000 in 1991 with 10% homogolated. The guidlines for rallying are very strict and closely monitored!! ( bearing in mind the chassis numbers started at 000102)
I'm just going by chasiss numbers and a small amount of logic, ,
im not saying im wrong, (but what I have personally reasearched I think i'm not far off the truth )
At the end of the day ( or YEAR as the case may be ) mine is the last official RB built no matter what you say