So I decided to make a bunch of gases to play around with for Mad Gasser. I started making the gasses one by one. Just before I got to White Gas, I got the Gas Collector trophy. "Huh, I must've had that on me already," I thought and then went on to sniff, inhale, et cetra gasses. And I couldn't find any White Gas on me. I even used the "Where did I put my stuff?" feature at http://startlingfecundity.com/me/inventory to try to find it. Nope.
Near as I could tell, I didn't have any. So I went ahead and created some White Gas. Now the API tool could find it. I smashed it and finally got the Mad Gasser achievement, but that oddity stuck out in my mind. It seems like somehow White Gas got left out of the Gas Collector trophy requirements. Not a big deal really, just a bit of an inconsistency.