That's what 24 bit format is for.
It's a very large dynamic range and quite forgiving.
If your worst case is making a 21 bit recording...
That raw track is higher quality than CD right out of the box with that. There's no problem to avoid.
You could make a recording that peaks at -36db and you'd still have an 18 bit recording. Still better than CD format. That would look like a blank flat line down the middle of the item at -36db. You have working room!
And for a final release format, you can have really really really quiet sections in the music and still have 8 to 12 bits of resolution. This is where 16 bit CDs maybe get grainy sounding. But I digress.
Anyway, the thinking is that if the meat of an incoming signal is -18db rms then it's very unlikely to get an over because that would be really really dynamic!