For Italian runner Gianclaudio P Marengo, Sunday’s New York City Marathon turned from a 26.2-mile race into an odyssey that ended on Tuesday when he was found on the subway still in his running clothes.

One asterisk on his journey: he wasn’t registered for the marathon. He ran while wearing someone else’s bib.

This is a constant worry and logistical headache for race directors, especially if a runner in someone else’s bib gets hurt during the race.

“If they’re non-communicative, we’ve got a real problem if they’ve got somebody else’s bib,” said Brant Kotch, president and race director of the Houston Marathon.

Marengo was found two days after the marathon on the New York City subway. Photograph: AP

The New York City Marathon bib has three ways its runner can be identified: the runner’s number, information hand-written on the back of the bib (if the runner chooses to fill that in), and a bar code that, when scanned, shows whatever the runner provided upon registration, including name, emergency contact, primary language, and any additional medical information the runner feel officials would need to know.

“The situation could also cause confusion and fear for friends and family of an unregistered runner since race officials aren’t able to track the status of a runner on the course in the medical tent who isn’t properly identified,” said Virginia Brophy Achman, executive director of Twin Cities in Motion, which puts on races that include the Twin Cities Marathon in Minnesota.

Running under someone else’s bib can also affect competitive results for everything from age group awards to, in the case of the Twin Cities Marathon, the USA Masters Marathon Championships. “We had an innocent situation in one of our smaller events where a husband and wife got bibs mixed up between them and he ‘won” the women’s race,” said Brophy Achman. “It got sorted out in the end, but the situation wasn’t something the actual winner needed to bear.”

Some races also ban runners who are involved in bib switching. In 2014, the winner of the Marine Corps 17.75 race was disqualified for wearing someone else’s bib, and both he and the person who gave him the bib were banned from entering any other Marine Corps Marathon-related event for the rest of the year. In its rules of competition, the New York Road Runners, which puts on the New York City Marathon, says that they ban big giver and bib taker from subsequent NYRR events. The Houston Marathon bans both for two years.

Kotch, who is also an attorney, said there could also be legal repercussions if a runner who didn’t sign their electronic waiver at register got hurt and tried to sue the race. “I don’t know if that waiver is still effective,” he said.

Some races, like the Marine Corps Marathon, Pittsburg Marathon and Broad Street 10 Mile Run, allow entrants to transfer their bibs to another runner before the race. The New York City Marathon does not have such a program. However, organizers allow runners to defer their entry to the following year, though they must pay the fee again, which for 2015 was $255 for US runners and $347 for international runners.