Clarification: Per My April 17th Interview with Kip Sullivan, Is the ACO Program Reducing Medicare Spending?

Per my April 17th conversation with Kip Sullivan concerning the Medicare Shared Savings Program/MSSP (ACOs), I noted an August 2017 OMB report that concluded the MSSP saved a net $1 billion in its first three years, i.e., gross savings, OMB reported, equaled $3.4 billion, losses (or reimbursements above benchmarks) equaled $2.4 billion, for a net savings of $1 billion.   OMB also reported, however, CMS paid out $1.3 billion in earned shared savings thereby implying the program lost $300 million. 

I've disputed whether the MSSP actually lost $2.4 billion for several reasons including moreover there's no comparison group and we cannot know what these providers would have spent, the counterfactual, had they not participated in the ACO program.

In back and forth with Mr. Sullivan subsequent to our discussion, he has made the very valid point that if we cannot know if the program lost money we cannot equally know if it produced Medicare savings.