What about Mehran Karimi Nasseri? I apologize for the quote being from wikipedia

but I don't have the time to find a more reputeable site as I'm heading to bed . . .
Nasseri claims he was expelled from Iran in 1977 for protests against the Shah and after a long battle, involving applications in several countries, was awarded refugee status by the United Nations High Commissioner for Refugees in Belgium. This allegedly permitted residence in many other European countries. However, this claim has been disputed.[3]
Having claimed to have one British parent, although he has produced no evidence to support this, he decided to settle in the UK in 1986, but en route there in 1988, his papers were lost when his briefcase was stolen.[4] Despite this setback, he boarded the plane for London but was promptly returned to France when he failed to present a passport to British immigration officials. He was initially arrested by the French, but then released as his entry to the airport was legal and he had no country of origin to be returned to; thus began his residency at Terminal 1.
His case was later taken on by French human rights lawyer Christian Bourget. In 1992, a French court ruled that, having entered the country legally, he could not be expelled from the airport, but it could not grant him permission to enter France.
Attempts were then made to have new documents issued from Belgium, but the authorities there would only do so if Nasseri presented himself in person. However, under Belgian law a refugee who voluntarily leaves a country that has accepted him cannot return. In 1995, the Belgian authorities granted permission for him to return, but only if he agreed to live there under supervision of a social worker. Nasseri refused this on the grounds of wanting to enter the UK as originally intended.[4]
Nasseri's stay at the airport ended in July 2006 when he was hospitalized and his sitting place dismantled. Towards the end of January 2007, he left the hospital and was looked after by the airport's branch of the French Red Cross; he was lodged for a few weeks in a hotel close to the airport. On March 6, 2007, he transferred to an Emmaus charity reception-centre in Paris's 20th arrondissement. Since 2008 he has continued to live in a Paris shelter.[4]
During his 17-year-long stay at Terminal 1 in the Charles de Gaulle Airport, Nasseri had his luggage at his side and spent his time reading, writing in his diary, or studying economics.[5] He received food and newspapers from employees of the airport.
Real life case no idea if he was telling the truth about his papers being stolen but the guy spent 17 years living in an airport because he "didn't exist" as far as the legal system was concerned.
As for the SINless being low numbers mentioned earlier that would actually lend a certain degree of realism as far as I see it to the whole distopian angle. A massive SINless population can't really be ignored but one that small I can see the people possessing SIN's not really being concerned "Its not a big problem, I rarely see a homeless person and I commute outside the arcology."
Finally and yes I am jumping all over, in Australia today there are young people who don't want to work because welfare takes care of their "needs". They would rather not get a job and income because they don't want anything more than to drive their car on dirt trails and hang out at Macca's. Now SINless don't get welfare but a small "tribe" who hunt and sing songs around the garbage can fire could evolve. Not just a group of homeless people in the same area but a tribe friends, family, sticking together working together to survive the matrxi crash, wars, weird and frightening events that acompanied awakening. That is . . .
Generation 1: Lose everything and huddle together to survive as the entire country implodes (great ghost dance).
Generation 2: Grew up amidst the "ruin" of America.
Generation 3: Never knew anything different and don't want a SIN because why do they need it? To vote? They don't care. To work? Hunting rats in the barrens doesn't need a SIN. To own property? Those SINners don't look happy at all.
First generation lost it and didn't think it ever came back, second generation grew up with only vague childhood memories of citizenship, third generation don't want to leave their homes and lives.