You can’t sing a harmonically complex song without ruining the surprise.
If your choir is working on harmonically rich or modulatory music, part of the fun is the surprise you will get to give to an audience when it’s performed. Those harmonic moments are what make the music exciting.
There’s also what make the music difficult, because at least at first, they are surprising to the singers as well as the audience.
The process of perfecting the music is the process of ruining the harmonic surprises so that they come naturally and perfectly tuned. Indeed, I think that you have to go beyond knowing your notes to having at least some understanding of what the harmonic expectation is and how you are mixing it up. Without that knowledge, you aren’t able to perfectly present the music to the audience for them to enjoy. And be surprised.