Faced with a 4-note chord with the three voices, the 5th is the usual one to ignore. For meatier chords (you shouldn't see many in Motown though) the other would be the root.
The floodgates of useful, informed advice have opened, thanks one and all. There's plenty for me to think about and build on
Well this section is two saxes and a Bb cornet whose softer tones don't cut through like a trumpet but nevertheless the combo can sound OK.
Given the vagieries of amateur live performance and unpredictable sound engineering, I have been trying to make the horn section audible across the range. I've tried C/A/T, C/A/B, C/T/B, C/T/T. The bari is ace in some numbers: e.g. Harlem Shuffle, where there's space for it to be heard doing the
beetroot thing but it is lost in others
It's interesting to learn that I may well be hearing enharmonic notes more often than I thought credible in Motown numbers
Declaration of interests: I live near the Tweed
There are several fantastic iconic books:If you really want to get to a complete understanding of the topic Sammy Nestico's Complete Arranger is IMO the best book on teh subject. It has lots of core examples with CD music of them happening. Every instrument's range and strengths are clearly set out.