Seriously? Is this a petty game of semantics?
Whatever is not banned here, can be called legal:
This is especially the case for a common substance that was discovered in 1905, and a supplement that has been commonly available and widely used for decades. We don't speak of some exotic designer drug that fits in a loophole.
"Where can I find this list of legal supplements approved by WADA?"
LOL, it doesn't exist. You claim it is legal. Where is your list?