Saw a play one time at Passe Muraille and it had a few different music cues including some amazing jazz music sounding exactly like sectional pieces from large ensembles like Count Basie. I looked on the program later to see who did the music and one local composer was credited for everything. Concluded that they were either a genius who can simulate the recordings and arrangements from the rich history of jazz more precisely than anyone I ever heard in 30 years, or they got 20 friends to play and record for free.. or they use samples (long complex samples) and call that their composition.