Luke, why not give us some items from your no doubt huge score library.
I might do that later. Problem is, my scanner is broken, and as you've said, photoing, cropping etc. takes time. Also, I'd like to choose good samples as you have done - what would be the point of choosing obscure things that don't give anyone a chance: it needs to be pitched right. I will think on...
Good for you! it's from 7. I thought that endlessly repeated trombone figure would give it away.
Ah, of course - you're right, that trombone figure should have given it away (it's amazing how similar some passages in Nielsen are, actually...). I've never seen a Pettersson score (

) so again I think it's interesting how the look of the print, as well as the notes themselves, made me think of something Nordic - is it a Hansen score?
As for the new ones...
18 - I thought of Verdi at first (contour of some of the melody) before I realised it was Carmen. But it's one of the bits that isn't in my score...
19 - is one of the Ligeti Etudes (Book II, L'escalier du diable).
20 - have to admit I searched for this one (googled the unusual, lengthy tempo marking), so I think I have the right answer [edit - I
know I have the right answer as I just listened to a sample at Amazon!], but I don't want to spoil it for those who might know it 'properly', so I won't say here.
My first thought, BTW, was Mendelssohn, but then I thought that, pre-Liszt, the tremolo is little used by real pianist-composers, more in transcriptions (which I momentarily thought this might be) and in music I tend to think of as less pianistic, so I ruled out Mendelssohn. The composer who it really is by is not a million miles from Mendelssohn, though.
21 - Stockhausen - Klavierstucke IX (again, the look of the score - Universal Edition style - is the first thing that I notice, then the notes and the language, though still all in the first glance, of course)
22 - that surprising measure of 5/8 is the clue - it's that famous 'first' of Handel's, Orlando's mad scene IIRC