I'll shoot the gunner first!
I don't think they actually record the vocals "live", I always had the idea that Bruce does it on his own after the instruments have been tracked.Bruce never sounds bad on Maiden's studio albums. And didn't they record the last 2 in a similar "live" fashion? So, I'm sure any mistakes made by Bruce got re-recorded until they sounded good. Maiden knows what they're doing so no worries here.