An Inverted Jenny Surfaces. The Flawed Stamp Had Not Been Seen Since 1918.

By James Barron

An Inverted Jenny stamp, with a biplane upside down, is considered one of the most valuable stamps in the world. This one has been owned for decades by a family in Illinois.CreditCreditChang W. Lee/The New York Times

No. 49 of 100 Jennies famously misprinted with an upside-down biplane was locked away in vaults for generations. The whereabouts of No. 66 remains unknown.

An Inverted Jenny stamp, with a biplane upside down, is considered one of the most valuable stamps in the world. This one has been owned for decades by a family in Illinois.CreditCreditChang W. Lee/The New York Times

When the phone rings at the nonprofit Philatelic Foundation in Manhattan, sometimes it is a caller claiming to have a rare stamp and wanting the foundation to authenticate it.

In the internet age, the people at the foundation can ask for a cellphone photo of the stamp in question. Usually someone from the foundation calls back and says something like, “Sorry, your stamp is not what you think it is. It’s not that special.”

But a recent call from Illinois got their attention. The man on the phone said he had one of the most famous stamps in the world, an Inverted Jenny with — oops — the airplane upside down. When the man sent a cellphone photo, the foundation’s curator, Lewis Kaufman, suspected the stamp was an Inverted Jenny that disappeared from sight soon after it was printed in 1918. Only 100 Inverted Jenny stamps exist. Mr. Kaufman suspected it was No. 49, one of only two that remained unaccounted for.

He handed the photo to his boss, Larry Lyons, and said, “I think it might be genuine. You ought to call this guy back.”

Larry Lyons, the executive director of the Philatelic Foundation, traveled from New York to Chicago to verify the authenticity of the Inverted Jenny.CreditChang W. Lee/The New York Times

Mr. Lyons, the foundation’s executive director, called. The man in Illinois said the stamp had been in his family for generations, most of the time in one safe deposit box or another.

To stamp experts like Mr. Lyons, No. 49 was an unusually treasured find. It was in pristine condition. It never had a gummed hinge affixed to the back, for mounting in a stamp album. It was never recut and reperforated, as one Inverted Jenny was after it was stolen. It was never sucked up by a vacuum cleaner, as another was. It was never put in a locket, as still another was, as a present for an owner’s wife.

Most of all, it was never resold, although Mr. Lyons suspects the man is considering selling it.

So for 100 years, No. 49 remained off the radar, to use an expression that did not come along until decades after the Jennies had captured the public’s imagination. A 1986 book that tracked each of the 100 Jennies had this entry for No. 49: “No record.” No. 49 has been a black hole on a Jenny website set up by Siegel Auction Galleries, a Manhattan firm that has sold many Jennies over the years.

Mr. Lyons said the Illinois man’s 91-year-old father had been a stamp collector, but the stamp had come from his mother’s side of the family. A great-uncle apparently bought it after the sheet of 100 was broken up, and after the great-uncle died, the great-aunt left it to the man’s mother in the 1930s.

Only 100 Inverted Jenny stamps ended up in circulation and two remained unaccounted for before the Illinois family revealed that they had one, No. 49.CreditChang W. Lee/The New York Times

“It spent all those years in bank vaults, which was a good thing for the stamp,” he said. Mr. Lyons said the man, who has asked not to be identified, could not explain why his father never put it in an album with his other stamps.

Inverted Jennies are not the most expensive stamps in the world — that title belongs to the one-cent magenta from British Guiana, the only one of which sold for $9.5 million in 2014. But Jennies can be pricey. No. 58 sold for $1.35 million in May 2016, according to the Siegel website. Three that had small flaws have changed hands since then, for far less money: No. 79 for $299,000 and No. 28 for $389,000, both in February of last year, and No. 76 for $295,000 last May.

No. 76 was stolen at a stamp show in Norfolk, Va., in 1955. It had been one in a block of four that belonged to the daughter of one of the founders of Dow Jones & Company. Who made off with the block, and who separated them into single stamps, remains a mystery. No one has ever been arrested. Of the four, only one, No. 66, remains missing.

No. 49’s story, like that of No. 66, began when no one at a government printing plant in Washington noticed the problem with the planes appearing upside down on a single sheet of 100 stamps among thousands printed in May 1918. But a financial clerk named William T. Robey noticed when he went to a Washington post office during his lunch hour soon after the biplane stamps became available. The clerk handed him the sheet of Inverted Jennies.

Some Inverted Jennies have sold for over $1 million.CreditChang W. Lee/The New York Times

He paid $24, the face value of the 100 stamps. He knew what he had. He left the post office as fast as he could and rebuffed postal inspectors who came looking for him, trying to get back what, to their bosses, were bloopers.

He soon turned a profit of $14,976, selling the sheet of 100 stamps for $15,000, enough to buy a new car, which he drove through the back wall of the garage that came with a new house. Or so the story goes.

The dealer he sold them to quickly resold them, for $20,000, but not before writing little numbers on the back of each stamp. The number “49” was visible on the stamp in the cellphone photo.

“The owner was even afraid of handling it,” Mr. Lyons said. “He asked me to come and get it. I said, ‘Put it in a FedEx envelope and send it to me.’ He said, ‘I’m not doing that.’”

Nor would he schedule a trip to New York, Mr. Lyons said. So Mr. Lyons flew to Chicago.

He accompanied the owner to a bank where the stamp lay in a safe deposit box in a Mosler safe. That was an appropriate coincidence: Gustave M. Mosler, who was president of the American Philatelic Society from 1929 to 1931, was part of the family from the safe-manufacturing company.

“He said, ‘You take it out,’” Mr. Lyons said. “That’s when I realized exactly what it was. I had a big magnifying glass with me, and the colors were so fresh. And then I turned it over and saw the 49 and went ‘Jackpot.’”

A version of this article appears in print on , on Page A18 of the New York edition with the headline: Rare Flawed Stamp, No. 49 of 100 Inverted Jennies, Surfaces After 100 Years. Order Reprints | Today’s Paper | Subscribe