Hey jb,
I too have had black cardamoms in some of the curry's I have bought from local IRs.
Have found one once in a Butter Chicken and also a Rogan Josh.
They aren't always in each curry though, so I am surmising from the lesson that I had, and it is a bit of a jump, that like what we did with the 3 different gravies, whole garam masala pieces are in the bases of curries here in some IRs here in Australia.
When they take the sauce from the different pots to make the end dishes sometimes a pod or piece of cassia bark will find its way through to the end dish. They can't be putting it in each individual curry as you would then find it in that curry each time you bought it.
Looking forward to some more of your lesson posts too, nudge nudge, wink wink.
Cheers,
Mark