Don’t know about that; our exchange continually bugs us for immigration or citizenship documentation although we are natural born or citizens for decades. Must be a state by state vs. federal exchange thing.
You may be right. I thought I remember articles back during the initial registration year (2013??) that noted the Govt wasn’t going to require proof, just say so and you get the subsidy. The objective was to get as many signed up as possible to reach their sign up targets. Perhaps you’re right, could be a state by state thing.