"We guess he [his grandfather] stuck them in the attic and forgot about them," Kissner told The Associated Press. "They remained there frozen in time."
The cards -- which contain legends like Ty Cobb, Honus Wagner, Cy Young, Christy Mathewson and Connie Mack -- are from the rare E98 series issued around 1910. Though it's unclear who manufactured the series, it contains just 30 players, half of which are Hall of Famers.
"It's like finding the Mona Lisa in the attic," Kissner said.
Upon the initial discovery, Kissner let the cards sit for two weeks before looking further into their potential value. After some research indicated the family might be sitting on something pretty special, he sent eight cards to expert Peter Calderon at Heritage Auctions in Dallas.
Calderon was taken aback by the sight -- and condition -- of the collectibles. They then sent all of the cards to Professional Sports Authenticator. The company, which had previously authenticated fewer than 700 E98s, said this particular series was the best it had ever seen.
"I was in complete awe," said Calderon."You just don't see them this nice."
The highest grade, on a 1-10 scale, the company had ever given an E98 Ty Cobb card was a seven. Sixteen different Cobb cards in Kissner's bunch ranked a nine. The startling find even contained a Honus Wagner that was judged a perfect 10, a first for the company when it comes to E98s.
As for the next step, the 37 best cards from the collection are expected to fetch $500,000 at an August auction during the National Sports Collectors Convention in Baltimore.
The Hench family is evenly dividing the cards and money among the 20 cousins named in their aunt's will. The majority have agreed to sell their share of the cards, which Heritage Auctions plans to sell over the next two or three years through auctions and private sales to avoid flooding the market.
In all, the contents of that dusty box from the attic are expected to bring in somewhere between $2 million to $3 million.