The Pakistani, widely regarded as the greatest player of all time, went five and a half years without losing between 1981 and 1986.
Rod Gilmour, co-author of 'Jahangir Khan: 555', said: "We believe that it could be significantly lower."
However, ex-world number one Jahangir, 52, reckons the tally "could be more".
He added: "The 555 figure should only be my tournament matches. I played invitational, exhibition and challenge matches.
"It could be between 600 to 700 matches if you include the others. Because I wasn't losing those either."
Jahangir won the World Open six times and the British Open Championship 10 times in succession between 1982 and 1991.
Gilmour and Alan Thatcher have researched record books, annuals, magazines and newspaper reports in writing their book.
"I grew up reading reports of Jahangir Khan and even then he seemed a mythical, magical figure to me," said Gilmour.
"There were no statisticians at the time chronicling his matches and not once has the figure been highlighted in press reports of the time."
Jahangir, whose winning run was ended by Ross Norman in the 1986 World Championship, retired in 1993.
The authors do not dispute the timeframe, but Thatcher said they "wanted to solve for accuracy's sake" the final tally.
He added: "The real figure? It's hard to say.
"But it could be lower than 500, which would mean that Dutch wheelchair tennis great Esther Vergeer could lay claim to the record."
Vergeer, who won her fourth consecutive Paralympic singles gold in London in 2012, went unbeaten for 10 years, winning 470 matches before retiring in 2013.
Squash legend Jahangir Khan's winning run of 555 matches - a record in any sport - has been questioned in a new book.