Only two examples? You guys can do better then that.
My point is that bus saturation is "generally" over-estimated as a problem. Of course it "can" happen. I designed one recording console with over 100 stems feeding the L/R bus. it can happen.
Looking at your 4 vocals singing at the same time... ASSuming the worst case summation (if they were making exactly the same signal, they don't) it would sum to 4x or +12dB. So if the bus was capable of cleanly passing +20dBu that means every vocal was peaking above +8dBu at the same exact instant. If the signals were not coherent they would only increase 2x or +6 dB meaning every vocal would have to be peaking to +14 dBu simultaneously... lets split the difference and say they were probably hitting +11 dBu each,, so pretty hot for a single stem, let alone a 4 part vocal harmony.
This is why we put meters on buses, and when no meter is budgeted, at least a bus clip light..(while some value products may not even indicate there).
Like I said if it sounds OK and no clip lights are flashing, it is OK. If you hear audible clipping like Ivan did, find it and fix it. It's not like the old days when we wanted to hit the mix bus hot to get decent S/N. While some may not have gotten that memo yet.
JR