"They always had some sort of logo on the uniforms back then," Shieber said. "That was nowhere to be seen on this. It was a very blank jersey and that disturbed me. My thought was I wasn't super comfortable displaying it."
But after the jersey was pulled from the display, another Hall of Fame curator made a startling discovery.
"She noticed something that not only I and every other curator had missed, but the millions and millions of people that have walked by this jersey since the 1950's had missed," Shieber said. "There was this extremely faint NY on the front, it was like a shadow of where a flannel NY used to be. We had just missed it, but once you see it, you couldn't miss it. That NY totally matched with a logo that was used for a small number of years, and the Spalding tag was also for a small number of years.
"So where that matched up, nailed it to one year -- 1905. The jersey went from probably-his-but-not-for-sure to one of the most extraordinary jerseys in our collection."
The rare jersey, worn by Mathewson in 1905 when he went 31-9 with a 1.28 ERA and 32 complete games, is one of more than 100 items on display at the Hall of Fame's exhibit at the MLB FanFest in St. Louis for the 80th All-Star Game on Tuesday night.
Among the more than 100 items and artifacts that the Hall of Fame brought to town are 24 St. Louis Cardinals-related items, including Mark McGwire's bat from his record-breaking 62nd home run and cleats worn by Ozzie Smith in the 1982 World Series.
More than 90 percent of the 35,000 three-dimensional artifacts at the Hall of Fame are in storage, meaning some fans will never see almost nine-tenths of their collection if they travel to the museum in Cooperstown. Most of the Cardinals items were pulled from storage and are being shown publicly for the first time in a while.
"We always try to tailor it to the home city," said senior director of exhibits and collections Erik Strohl. "There are things in the exhibit that are for the baseball aficionado that maybe the casual fan hasn't heard of, but certainly items from modern day, where kids coming to the exhibit will see names like Albert Pujols, Wade Boggs, Cal Ripken -- names that are familiar today.
"If you're coming to FanFest and you say, 'Well, I've already been to Cooperstown, so I want to focus on something else,' you really need to come to the exhibit, because you will get to see a lot of stuff that doesn't go on display much. Some of the city-related things come off display because we want to bring some of these recent things, like Pujols and [Yadier] Molina and Tony La Russa and Mark McGwire."
A 1952 Stan Musial jersey is on display at FanFest, as well as sunglasses worn in the 1930s by James "Cool Papa" Bell in the Negro Leagues. Bell, who was inducted into the Hall of Fame in 1974 by the Negro Leagues Committee, is highly regarded as one of the fastest players in the history of baseball. Bell was clocked running the bases at just 12 seconds, the fastest ever recorded at the time.
"He was known for honestly doing things like going from first to home on a single and second to home on a bunt," Strohl said. "He would play the outfield so shallow in center field that you couldn't get a hit off of him because, if you tried to hit it over his head, he would run back and still probably catch it at the wall. The most famous story was that he could flip off the light switch and be in bed before the lights went out, which it turns out was true because he was playing with the light switch and realized there was a faulty circuit and it didn't turn off right away."
The Hall of Fame's exhibit is always one of the most popular at FanFest, with fans pausing to look at each of the six different cases representing an era in baseball history.
From the 1930 Babe Ruth Yankees jersey to the hat that La Russa wore for his 2,000th career win, there truly is something for all generations.
"Interacting with them is fun, but just watching generations of people act together, you see a grandfather, a son and a grandson come to FanFest together," Strohl said. "And that really underscores and shows how much of a generational sport that baseball is, how baseball has a much wider history and a much more embraced history than any other sport.
"But also seeing people maybe learn something that they didn't know about or haven't seen before -- if you watch people have dialogue about something and you sit back and watch people become engaged by your exhibit and therefore discuss it, as a curator, there's nothing more fulfilling."
B.J. Rains is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.