I recall reading that Powerslave was 2 or 3 Bruce songs combined into one that Steve helped with, as for solos guitarists often dont get song credits just for laying one down, thats not exclusive to MaidenIf you're talking about lead parts like Trooper main melody, that's Steve. From what he know he whisles this stuff out while playing the roots on the bass. If you're talking small texturing like Smith does on Trooper chorus, or a lot of it on CSiT chorus, I really can't know. Maybe it's his original idea maybe guitarist came up with it in preproduction jam.
For me weirder is Powerslave solo Dickinson credit, because the only way he could've conveyed that instrumental section is by reffering to another songs (like he asked Nicko to do 'the thing' from Pat Travers track) and ask Dave and H to pull up something akin to that. And we know there are different takes around (the Iron Curtain video), so solos were developed as opposed to improvised over a chord sequence Bruce set there. For me it is utterly stupid to not credit guitarists for those solos, but it's likely that the harmony section in between H's and Dave's second solo was simply sang out by Bruce. That line has his phrasing written all over.