NEW YORK (NYT NEWS SERVICE ).- Dorothy Seymour Mills, who collaborated for more than 30 years on a landmark three-volume history of baseball with her first husband, Harold Seymour — although he refused to credit her — died on Nov. 17 in Tucson, Arizona. She was 91.

Her friend Charmaine Wellington said the cause was complications of an ulcer.

The Seymours’ work, which traced organized baseball from its roots until 1930 in the first two books, then detoured to a focus on amateur baseball in the third, has long been considered the first significant scholarly account of baseball’s past.

“No one may call himself a student of baseball history without having read these indispensable works,” John Thorn, Major League Baseball’s official historian, wrote in Baseball Research Journal in 2010.

Mills played numerous roles in the creation of “Baseball: The Early Years” (1960), “Baseball: The Golden Age” (1971) and “Baseball: The People’s Game” (1990). She was their primary researcher, scouring libraries and archives throughout the country; she organized the project, edited the books before they were submitted for publication, typed the manuscripts and prepared the indexes; and she wrote a large part of the final book.

Yet each volume bore only Seymour’s name. When the first book was published, Sports Illustrated compared him to Edward Gibbon, author of “The History of the Decline and Fall of the Roman Empire.”

In each book, Mills was simply one of many people thanked in the acknowledgments. In “The “Golden Age,” Seymour cited her for having “contributed her knowledge and professional skills to all phases of the work.”

For her, the collaboration was far from satisfying.

“At once glorious and ignominious: That characterizes my work with Dr. Harold Seymour,” she wrote in “A Woman’s Work: Writing Baseball History With Harold Seymour” (2004).

In 1989, as they were nearing completion of “The People’s Game,” Dorothy Mills formally pressed her husband for co-author status. Seymour’s declining health meant that she had done more than usual. She had also written the last 13 of its 37 chapters.

She presented him with a 12-point demand for recognition.

In her second point she wrote, in part: “I sifted, analyzed, and organized all the research, putting it into a form that would make it intelligible and from which the writing could be done. I produced hundreds of pages of outlines interpreting as well as quoting from the research.”

She added, “Without this analytical study, the writing would have been impossible.”

Seymour denied her.

“Everyone assumed that he had done all that work by himself — that’s what he wanted them to assume, but we were equal partners,” Mills said in an interview with The New York Times in 2010. “He just couldn’t share credit. I didn’t say anything at the time, because at the time, wives just didn’t do that.”

Seymour’s resistance to sharing credit was similar to that of the historian Will Durant. Through the first six books of his 11-book series, “The Story of Civilization,” he did not share credit with wife, Ariel. But he changed his mind in time for the seventh volume.

It would take nearly 20 years after Seymour’s death in 1992 for Mills to get her due.

Dorothy Jane Zander was born on July 5, 1928, in Cleveland. Her father, Henry, was a printer. Her mother, Katherine (Reinert) Zander, was a homemaker.

By her high school years, Dorothy was smitten by the English language, its grammar and history, and by the authors Upton Sinclair and Thomas Mann. With an eye on a journalism career, she edited her high school newspaper and was a clerk for The Cleveland News.

At Fenn College (now Cleveland State University), she studied English and met Seymour, 18 years her senior, who was her professor for history courses. While she was still a student, Seymour hired her for secretarial work and began using her writing skills to help him prepare his courses. Soon, she started helping him with his doctoral dissertation on early baseball history.

He was a baseball fan — he had been a batboy for the Brooklyn Dodgers at Ebbets Field — and she was not.

“People can’t understand that,” she told The Times. “I think it’s a good idea to remain above that. You write a lot more objectively about a subject you’re not in love with.”

They became increasingly close and married after her third year at Fenn. She transferred to Western Reserve University and after graduation became an elementary-school teacher.

Seymour received his Ph.D. from Cornell University in 1956, then earned a contract from Oxford University Press to write the first volume of the “Baseball” history. She left teaching after they began work on the second volume; in her free time, she wrote “Ann Likes Red” (1965) and other children’s books.

Their collaboration continued, and she went along with not receiving credit. But she eventually became frustrated and presented Seymour with her demands. She later recalled how difficult it had been to speak up.

“It was too easy not to,” she told The Times in 2010. “I was just playing my role. I was just doing everything I had done before and continuing with it. I was comfortable with that role.”

After Seymour died, she began to publicly discuss her role in his work, and to write about it. But nearly two more decades passed before her name was finally on the baseball books.

It began with another vexing reminder of her husband’s refusal to credit her. In 2010, the Society for American Baseball Research (SABR) announced that Seymour — not Mills — would be among those receiving the inaugural Henry Chadwick Award, which honors baseball researchers.

“It was kind of unbelievable,” Leslie Heaphy, a vice president of SABR and professor of history at Kent State University, said by phone. “Really, you’re not going to give it to her?”

After objections from many of SABR’s female members, the selection committee reversed itself. Mills was added to the list of awardees.

Four months later, Oxford announced that future printings of the “Baseball” trilogy would bear Mills’ name. The books were reissued the next year — with her name above Seymour’s on the cover of “The People’s Game.” (Her prominent role as co-author was confirmed in a study of 71 boxes of the Seymours’ notes by Steve Gietschier, managing editor of research at the Sporting News, and accepted by SABR.)

By then, Mills’ life had changed significantly.

She had met and married Roy Mills, a former officer in the Royal Canadian Air Force, in the 1990s. And she wrote historical novels, including “The Sceptre” (1998), about an Austrian immigrant living in Cleveland who returns to her homeland and there unravels a Nazi plot to kidnap the conductor Arturo Toscanini, and “Drawing Card” (2012), about a woman who is not allowed to pitch in organized baseball.

She was also the author of “Meatless Meat” (2001), a book of vegetarian recipes; a series of mysteries set inside an assisted living facility like one where she lived; and “Chasing Baseball: Our Obsession With Its History, Numbers, People and Places” (2010). She sometimes wrote under the name Dorothy Jane Mills.

Mills, who lived in Tucson, is survived by her stepdaughter, Mary Jane Webb; her stepsons, David, Kenneth and Donald Mills; and six grandchildren. Roy Mills died in 2012.

In 2011, Mills recalled her joy at Oxford’s decision to add her name to the baseball books.

“Oh, it was very satisfying,” she told SABR in 2011 in an interview published on its website. “But I’d always had that pride, you know. Especially when Seymour was alive and the wonderful reviews were coming out. I knew that most of those reviews were partly because of my work.”

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