Sean Casten and Adam Stein have been discussing when it is important that a carbon savings be additional — that is, when it is important that we not pay for a saving that would have happened anyway. You guys are making this way more complicated than it needs to be.
Iron-clad additionality is critical when you’re selling a permission for someone else to pollute. If you are reducing emissions, generating a financial instrument from that fact, and then selling it to someone else to use as a substitute for reducing their own emissions, your reduction had damn well better be additional. Otherwise, you are almost certainly increasing pollution.