One of the things that makes Erroll's career fascinating is the fact that he couldn't read music. He had a remarkable ear, with the ability to hear a song once and then not only play it back, but immediately put his own unique spin on it. Improvisation was one of his greatest skills. He was well known for never playing a song the same way twice. In fact, he once remarked that he used the energy of the audience to help shape how he would play at a performance.
Why, then, would the collection even include sheet music? Though Erroll didn't use it, his bands did, and eventually many of his tunes would be orchestrated for full band or for others to play. The material in this section of the collection includes everything from lead sheets to full arrangements for orchestra, and includes the music for many of Erroll's greatest pieces.
A complete inventory of the arranged music in the collection can be found in the collection guide, Boxes 13-23.