Many were called. Few chose to respond.
The federal Obamacare insurance marketplace HealthCare.gov signed up 147,000 people in 36 states during a special tax season enrollment period, officials revealed Tuesday. That relatively light level of sign-ups was similar to what was seen in 11 other states and the District of Columbia during their own grace periods.
HealthCare.gov issued the final tally via Twitter rather than a press release or news call that Obama administration officials have previously used to announce other numbers and results.
The federal exchange's special enrollment period was open to people who learned they were subject to a tax penalty for failing to have health insurance coverage last year when they were preparing their tax returns.
In all, it appears fewer than 250,000 people signed up nationally. In Hawaii, no people—as in zero—signed up during the special tax season enrollment.
That national number could change slightly as New York has yet to release its final tally.
"We're finalizing that now," said a spokeswoman for New York's exchange when asked when its tally would be released.
The anemic results are in a sharp contrast with the nearly 11.4 million people who selected a health plan during open enrollment on Obamacare exchanges.
As a result, millions of people next tax season could owe potentially large fines for failing to have health insurance during 2015 that they might have avoided if they availed themselves of the special enrollment.
"In terms of awareness around the tax-filing special enrollment period, we know that generally knowledge of special enrollment periods is low," said Jessica McCarron, a spokesman for the Obamacare advocacy group Enroll America.
"Because there are fewer consumers who qualify for coverage than during open enrollment, outreach can be challenging. Especially since this was the first year that many consumers were understanding the tax implications of the law, the tax-filing special enrollment period was also new to consumers," she said.
However, McCarron said, the numbers compare "favorably" to other special enrollment periods.
"We're certainly happy about any opportunity for consumers to get coverage and it's great news that thousands more were able to enroll in health coverage for the rest of the year," she said.
The special enrollment periods were available in all but three states—Colorado, Idaho and Massachusetts—after open enrollment on Obamacare exchanges ended in mid-February.
The chance was offered by federal and most state exchange officials because of concerns that some people would face a double whammy after becoming aware they owed a fine for failing to have insurance during 2014 only when they prepared their tax returns for that year, after the open enrollment period for 2015 plans was closed.
In such cases, people could have ended up owing the higher of $95 per person or 1 percent of their household income as a fine for 2014, and then be unable to avoid a fine that rises to the higher of $325 or 2 percent of household income for 2015. But despite that potential financial hit, most people who were eligible for the grace period passed on the opportunity.
"I don't know how many people were really aware of it," said Katherine Hempstead, who directs health insurance coverage research for the Robert Wood Johnson Foundation. "I think people thought maybe this was going to be this big, teachable moment that people realized something that they didn't know before."
But, she said, in talking with people who had decided earlier on not to sign up for insurance this year, "The vibes that we got with people was that they had kind of run the numbers and looked at what their insurance was going to cost them, and what the penalty was going to cost them," and decided they would rather pay the penalty.
"It sounded more or less rational," Hempstead said. "They're rolling the dice on that point," she added, noting the risks of high health bills if one falls ill without insurance.
The best-performing state that released numbers for special tax season enrollment was California, whose exchange had signed up about 33,000 people as of April 28, but which had no final tally as of Tuesday, according to a spokesman.
"California was like the tallest leprechaun," Hempstead quipped.
Washington state had more than 16,000 sign-ups during special enrollment, but that tally included people who had other situations that allowed them to enroll after open enrollment. Maryland's exchange had 4,709 special tax season sign-ups, and Kentucky's had 3,047.
The District of Columbia's insurance marketplace has almost 1,400 special enrollment sign-ups, but did not break out a total for people motivated by the Obamacare penalty. Neither did Minnesota's exchange, which reported about 3,900 special enrollment sign-ups on Tuesday.
Read MoreDoctors 'reluctant' on Obamacare
Smaller states had even smaller enrollments during the grace period. Connecticut had more than 1,400 people sign up, but Vermont, where the grace period expires at the end of May, has signed up just 97 households.
"The fairly low number lines up with what we've heard anecdotally from tax preparers—not a lot of big surprises at tax time—and with the work we had already done to cut Vermont's uninsured rate nearly in half from 2012 to 2014, down to 3.7 percent," said Vermont exchange spokesman Sean Sheehan.
Rhode Island's exchange signed up just 25 households representing 32 individuals.
According to a spokeswoman for Hawaii's exchange, "To my knowledge, we have not reported special enrollment ... for this reason," when CNBC asked if there were any penalty-based enrollments. She later confirmed that no one signed up for that reason.
Open enrollment in Obamacare plans for 2016 will be even shorter than this year. The open enrollment begins Nov. 1, and is set to run through Jan. 31, 2016.
Some Obamacare advocates are concerned that the shorter window could again lead to surprises for people who will be unaware of how high the penalties are for going without insurance until well into tax filing season, and well after open enrollment ends. The penalty for failing to have coverage in 2016 rises to the higher of $695 per person or 2.5 percent of household income.