Read the code as more a contingency plan than a chronological timeline.
Sorry, missed this post. I get what you are saying, but they wouldn't have put a contingency plan in place in 1971-2 expecting 6cyl SL/R's not to sell. They'd simply have not built a 6cyl SL/R if they thought that might be the case. Plus they were a "just in time" manufacturer, so parts were procured for vehicles as they entered the schedule, so that the parts hit the assembly plants just before the car was due for assembly. There was rarely ever spare or redundant or left over parts as almost all parts were ordered off the production schedule. Sure, some raw materials became left over, like trim material, and GMH simply made special trim in later vehicles to get rid of it (like some HG with HK material). They were also subject to minimum order economics - on Engineering Change Notices where they price up changes/additions etc there is always pricing for varying quantities, but this was for special stuff like Tail-Tents (or Hatch Hutches) and other one-off items, not for sports dashes or wider wheels etc. It does appear that the Gpak decals were subjected to this, in Norms book on I think page 168 he says that there were 2500 Gpak's built in early 1975 but they weren't popular even at a few hundred $ less than an SL/R and had to ship them to NZ to try and sell them. They appear to have had more that 2500 decal sets, as they made another run of Gpaks late in 1975 to use up the decals, but they were a lot dearer by then.
I reckon the Gpak was one of Bagshaw's "I want" things, like the HQ GTS sedan, and given the consecutive option codes makes it more likely. He was famous for his "I want" things and getting them. The HQ GTS350 sedan was another, you can see by its XW8 option code it came after the XV2 SS and XV4 GTS sedan. He wanted the 350 and he got it. GMH had to reduce the number of planned GTS350 manual coupes to make it happen as by the time the XW8 became reality they only had about 100 engine/transmission sets left (there was only one batch of these engines and boxes for HQ ever delivered to GMH), and they'd used up half of those original destined for the HQ series run by the end of 1971 (HQ was supposed to be replaced by HV at the end of 1972 and there was to be no 350 in HV). The GTS350 sedan manual is the reason why the manual HQ GTS350 manual coupe was gone halfway through HQ production.