Nissan - just like everybody else - were changing the aero packages on their cars virtually on a race-by-race basis. One of the main difficulties with introducing new bodywork parts within the framework of the JAF/FIA Group 4 and 5 rules was that they had to be evolutions of already homologated parts. Any radical change - like the 'Grande Nose' itself - had to have a fresh homologation. It wasn't simply a matter of bolting parts on a car and going racing...
Who said the 'G-nose' was "the ultimate"? The HS30-H 'Fairlady 240ZG' was a homologation model, made and sold to the general public with the express purpose of legalising aero and body parts for JAF/FIA Group 4 racing. The road car didn't come with any front spoiler/air dam/splitter because it wasn't necessary for the homologation (such parts could be legalised for race use by adding them as evolutions to the homologation) and Nissan fitted a variety of different spoilers to its race cars. At that time it was tyre technology which was the main limiting factor in 'grip'.