Perhaps there is a very slight chance of water in the tubing becoming corrosive with the addition of CO2, but that wouldn't last long as the CO2 is extremely dry and this would flush out quickly. Obviously you'd never run Coca Cola through copper. Not for long anyway! But an inert, dry gas should be safe with clean copper. We leased a six ton CO2 receiver and installed it under the watchful eye of the owner/CO2 provider using copper exclusively--both L and M. That was more than 10 years ago, and to my knowledge it's still installed and working fine. I can't understand why any compatibility chart would recommend against it. I'd ask why to understand the underlying concept and also get a second opinion. And please post the results here so I can learn something! Good luck!