WISE, Va. - On a sunny Saturday at the county fairgrounds in this Appalachian community, the gaps in the American health care system were on vivid display.

Lured by the promise of a weekend of free checkups, surgeries and dental care, thousands of people turned up two weeks ago in the far southwest corner of Virginia, as shown in the video documentary that accompanies this article.

Many of those families would have much better access to medical help under the reform plans being debated in Congress. But a close look at the most recent data indicates even the most sweeping proposals are likely to leave some of them outside the safety net.

About 50 million people in the United States are now uninsured, according to new figures from the Congressional Budget Office. If an overhaul of the system is launched this year, as many as 17 million people would still be without health insurance by the end of the decade, according to preliminary analyses by the CBO.

Up to half of those falling through the cracks would be that portion of the working poor who make too much to qualify for free care or federal subsidies, but feel too cash-strapped to buy their own policies. Most of the rest would be undocumented immigrants.

The three-day free clinic that began July 24 at the Wise County Fairgrounds was run by a charity called the Remote Area Medical Corps, which gathers doctors and nurses who volunteer their services.

Whole families waited for hours in animal stalls set up as temporary offices for mammograms, diabetes tests and checks on various aches and pains.

Hundreds were shut out of eye and dental exams when doctors and medical staff were overwhelmed by the numbers. No one, among those interviewed, could afford to go elsewhere.

"The need has always been great. What we are seeing now, of course, are more people who have lost their jobs or lost their insurance," said Stan Brock, founder of Remote Area Medical Corps, which has been sponsoring clinics around the world and in the United States for two decades.

People at the Wise fairgrounds voiced conflicting thoughts about their status. Some openly feared a government takeover of health care. Others said they doubted that politicians could challenge the special interests that influence the cost and availability of treatments. All admitted they had no inkling if they would be better off after the historic overhaul.

All health care proposals now moving through the House and Senate are aimed at requiring people to carry insurance. People who fall below an expanded poverty line - $14,403 for an individual or $29,326 for a family of four. Families and individuals who earn too much for Medicaid would qualify for direct government subsidies to buy health insurance, either privately or possibly through a government-run option - up to an income cutoff level that is still being debated in Congress.

The Congressional Budget Office has calculated that subsidies could cost as much as $773 billion from 2013 to 2019.

But there are significant differences between the House and Senate over how much to spend on broadening the medical safety net.

The current House proposal would support subsidies for people with incomes up to 400 percent of the poverty level. That means a family of four earning up to $88,200 a year could qualify for some federal help to offset their premiums. An individual could earn up to $43,320 and qualify for some aid.

Talk in the powerful Senate Finance Committee has suggested a more restrained scale of help for those currently uninsured. People could qualify if they earn no more than 300 percent of the poverty level. That means $66,150 for a family of four and $32,490 a year for an individual.

People earning above those levels would begin to pay full premiums and deductibles - although under the current proposals they would be eligible for government aid if they had to pay more than 12 percent of their incomes toward health care.

Doctors familiar with the expectations and needs of the working poor said they are concerned about where the lines of assistance will be drawn. "There will probably still be some people who fall through the cracks," said Wende Kozlow, a staff physician at University of Virginia who has volunteered at the Wise clinic in previous years.

Those who just miss qualifying for the subsidy might figure it would be cheaper to go without insurance, pay the federal penalty - proposed to be up to 2.5 percent of their income - and hope they don't get sick.

"The House bill would help a lot...But the one emerging from the Senate Finance Committee troubles me," said Wendell Potter, a former health care executive who was motivated by Remote Area Medical's work to change his own career and advocate for reform.

Jennifer Tolbert, an analyst for the Kaiser Family Foundation who has monitored the shifting sands of the health care proposals, said the Obama administration has undertaken ambitious reforms. But, she said, universal coverage will be elusive no matter what legislation emerges in the coming weeks.

Some people will inevitably be left behind, Tolbert said, because "we're building on a flawed system."

Lagan Sebert is a staff reporter and Christine Spolar is senior editor at the Huffington Post Investigative Fund, an independent, nonprofit journalism venture based in Washington, D.C.