In New York, 59 percent of the nearly 343,000 private Obamacare plan enrollees reported being uninsured when they picked their plans. And 90 percent of the Medicaid enrollments via the state's exchange reported having been uninsured.
Read MoreWeb broker woos young Obamacare enrollees
The two states disclosed their data to CNBC on Monday and Tuesday.
New York and Kentucky are the only two states known to require that Obamacare applicants disclose their insurance status. Neither the federal government, whose HealthCare.gov exchange handles enrollments in 34 states, nor any of the other states that operate their own exchanges require Obamacare applicants to disclose their current insurance status.
The lack of data nationwide about the insurance status of Obamacare applicants has provided ammunition to opponents of the Affordable Care Act. Those critics argue that the majority of Obamacare enrollees appear to be people whose prior insurance did not comply with new ACA standards, and not the uninsured who the law was specifically written to help.
Read MorePricy drug concern 'just headlines'
A recent McKinsey study found that in February about 27 percent of people who had selected insurance plans from either the government-run exchanges or other sources had unidentified themselves as previously uninsured.