For spectroscopy, it doesn't matter if you know its chemical formula. It's like this, from what I understand: Color #1 is made with a certain combination of Red, Green, Blue (RGB). Color #2 is made with a different combination of RGB. Color #1 and #2 are very different but have the same basic component colors. Lets say you mix 30 such colors, each made from some combination of RGB, to produce Color X.

Can you really say if Color #432 is present in the mixture? You know its RGB combination. Nope. Because if it is very well possible for two different sets of 30 colors each to produce Color X in the end.

Carbon, Oxygen, Hydrogen are like the RGB of biological molecules. They're present in nearly everything. Trying to find a substance made entirely of carbon (like Graphene Oxide) in a sea of organic molecules is impossible with just looking at which component elements are present. But apparently there are other (non-spectroscopic?) methods to identify it, according to factdigger.

If you know what to look for it's cheaper (single test). But if they used something no one has heard of? You have to test for everything (thousands of tests). The only compound most people have heard of is Graphene Oxide, so everyone just latched onto that.

All we know is that the vaccine is not supposed to have anything react to magnetism, but it does. Japan rejected a batch for this reason. They claim it was a manufacturing error. Or maybe only certain batches are nefarious, so it looks like a random occurrence.