True
Some pieces that haven't been mentioned:
Finnissy - English Country Tunes (particularly mvts 1,5, and 8 ), Piano Concerto no. 4
Flynn - Trinity
Sorabji's TE no. 22 has some clusters at the end
Ligeti - Desordre, L'escalier du diable, Atmospheres (not piano)
Penderecki - A lot of the early orchestral pieces use microtonal clusters (eg. Symphony no. 1, Threnody)
Xenakis - Evryali
Messiaen - Some pieces from 'Vingt Regards' such as 'Noel'