Spencer recently told United Press International he was sorry he was the only lead who wasn't able to talk to the real-life guy he portrays in the musical about the legendary band.
Original member Nick Massi died in 2000.
"I just had to rely on our writers, Marshall Brickman and Rick Elice, because they had done extensive interviews with Bob Gaudio, Tommy DeVito and Frankie Valli and they had also spoken to Nick's family," Spencer said, explaining he also talked to Massi's friends and listened to tapes of his later work in an effort to capture the musician's spirit.
Spencer said Massi's relatives are extremely supportive of his endeavors.
"To have his family tell me I did their father justice and to have his nephews and niece come up to me after the show and give me a big hug and say, 'Thanks for bringing our uncle back to life for a couple of hours' -- that's the highest compliment ever."
"Jersey Boys" played its 100th performance Wednesday night.