There are many ways to Rome!
In theory one could change the output an BIOS in an way to disguise the real identity to some level. But as said before a guy not being able to flash a card would not be able to do such a hack. Nevertheless from an Apple Service Points perspective it would be interesting to "fool" customers to believe the got a original spare while in truth they got away with a much more capable (metal) GPU. Before digging deeper into the way macOS is working the approach would not really work. Drivers are selected based on the GPU installed and found within the system. The AMD and NVIDIA drivers are different. You cannot use gas for a Diesel engine.
To come around this "fooling" story I was thinking about using the genuine NVIDIA software tools, these are only available on Linux and Windows.
Using the very same Linux utility you can run the other command called
amdvbflash -i to check if the GPU is an ATI/AMD one as we all believe.
There is another way I used in the Big Sur patcher to autodetect the installed GPU using a simple a command with the terminal app from macOS:
Code:
me@iMac ~ % /usr/sbin/system_profiler SPDisplaysDataType | fgrep "Device ID" | awk '{print $3}'
0x6720
me@iMac ~ %
Possible outputs for the ATI6xx0 series are
0x6720 or
0x6740 or
0x6741.
But this is exactly the same command running to provide the output of About This Mac -> System report. Which already reports on your system a ATI 6970M card.
Are we going round in circles? We cannot write you into doing the tests. You have to start them on your own.