I looked at their discography a while ago and noticed they'd only released one record since 1982 and that was in 2006 - 13 years ago.
So basically everything they play is going to be classed as old music or Heritage if you want to be posh.
Just going back to Susan's
Kiss reference. It's only their last album they aren't playing anything from, an album they toured extensively at the time.
As for Maiden, the Legacy tour was one of their 'classic tours' - the ones they do when not supporting an album. When they tour an album they certainly give a large bulk of their set to said album. (I know, i've grumbled about it in the past
)