Date rape drugs are largely an urban myth, they do EXIST but the idea that women are being commonly drugged and raped by them is the myth.
And while I am unsure about the benzos used, GHB almost always comes in the sodium form and is incredibly salty like GRAMS of salt per dose. 2-4 grams is used as a dose, would anyone fail to notice grams of salt in their drink except maybe a bloody mary?
I guess it’s not technically completely impossible. Enforcement people have quick test kits that are engineered to indicate the presence of this or that - and false positives are possible.
I just doubt that this is more than a concept - that is, I doubt the actual chemistry has been worked out in any detail at all.