as for your stormtroopers... I'm not sure, but could you possibly have those broken uper leg plates as... well, broken upper leg plates? Already battle damaged stuff, because, you know, they're guard and they don't always get to be equipped with the new stuff. Having seen baatle and being shunted from one end of the conflict to another as the guard's 'elite', there might be a few who had not had proper resupply for their armour yet.
Or am I being silly now?
Anyway, don't be disheartened. We all make mistakes (hoo boy, do we all make mistakes), and that's something to learn from.
If all else fails (including the damaged armour idea), then practise the green stuff skills on them (if need be with someone from your local store) to see if you can fix it. If you're planning to not use them anyway because of the damage, all you can lose is some time. What you can gain is a ton of experience!
A few years back there was a conversion contest on another forum. Someone asked if I was to join in, and I said I couldn't do it, because I'd never done it before. So the guy said "if you never try, you'll never know. All the best sculpters here said that the fear of trying something is their biggest stumbling block". I tried, eventually built this Tervigon WIP
(hope you can see it), and am still happy with the result even years later.
The guy who encouraged me then is dead now, so in his memory I'll encourage you to try out your greenstuff skills! Or, you know, just use them as elite guardsmen with no recent resupply.