The British group’s fourth album, released in August 1987, was a three year production odyssey — and still relevant. — Def Leppard never left. The band first formed in 1977 in Sheffield, England and became one of the premier metal rock bands of the 1980s and beyond. They have endured through tragedy and triumph. Four fast facts: The band’s third studio album, Pyromania, was released in January 1983. It reaching…