How do you define a research chemical?
If the chemical is not "natural" it's an RC? Well, how do you know what's natural and what not? There are so many plants, fungi and animals in the world that we haven't analyzed yet. Amphetamine was thought to be man made up to a few years ago. Then it was found that a certain tree actually contains it, along with several other chemicals. And anyway, no one considers LSD a research chemical, although it is completely synthetic and doesn't occur in nature (as far as we know).
Or, if the chemical is new it's an RC? So how long does a chemical need to be used until it's no longer an RC?
Actually, I would say that in the end we humans understand so very little about any psychedelic that they should ALL be considered research chemicals.
By definition, a research chemical is a chemical that is being researched. So actually, one could even go so far as to claim that there is no chemical that is not a research chemical...