My tuppence.
Some of you will know that my son did the basics of an FEA (Finite Element Analysis) for Dave Silcock on his "non legal" cage which he had built from Chrome Moly, but failed to get the paperwork done on time before MSNZ moved the goal posts on the main hoop. As Sean doesn't have the applicable certification his numbers would not have been accepted. (He does do rather high powered engineering for a significant manufacturer of close to £2 million cars here in the UK). Out of interest he did a quick set on the MSNZ "approved" cage. Dave's one would pass the numbers which MSNZ required, the MSNZ one doesn't, and by quite a way.
As Ray says, they have no differentiation on "their" cage for if you are putting it in a Falcon or a Bambina, but when it came to the Jag, they wanted to include the weight of the car as a reason to decline.
Bashing heads against a wall comes to mind.