There's a lot of consternation aimed at Judas Priest's Unleashed in the East album, people claimed all the vocals were studio takes due to Rob Halford not being able to hit the highs notes. Maybe they were, but I called Bullshyte on that claim that he couldn't hit those highs, as I saw them on The Killing Machine tour in 78 and again at Donington in 1980 and he certainly had no problem hits those notes.
I saw Queen in Edinburgh in 1976 and again in Newcastle in '79, '79 was basically the Live Killers set list, they blasted through that set with no apparent problems, my only gripe was Brian May seemed like he was just going through the motions with the rockier elements. Whereas in '76 he was still a rock god! As for Thin Lizzy's L&D album, Producer Tony Visconti himself said most of it was redone in the studio, especially the guitars & vocals. I know that Southbound was recorded during the soundcheck, some of the songs on the album are actually from their gig at The Tower in Philadelphia in October 1977, hence they differ greatly from the video/DVD.