Back in the 70's, you used to be able to buy "Sketch Scores". Most sheet music was your basic piano/vocal/chords, but Chicago Anthology One (first four albums) and Chicago Anthology Two (V through VII) were also available as Sketch Scores. I think I picked up a standalone book for Chicago VIII as well.
Instead of the cheapo way most sheet music transcribes just the "main" parts of the songs, usually skipping the instrumentals and solos, and sometimes intros and outros as well, the Sketch Scores took more care to give you the whole song, with horn parts, background vocals, even bass parts if they were non-standard. Not a full score, but something you could read and play on the piano if you were so inclined, which I was. I was still in high school, still teaching myself piano, so cooking up my own solo piano arrangements based on chords, a melody, and condensed horn parts was a fun challenge, and I learned a lot about arranging by playing from sketch scores and having to extrapolate the rest.