You can easily discover if the nut is cut right - guide measurements here
https://www.talkbass.com/threads/nut-height-action.619581/?amp=1474037821
You’re right that there is no undoing it, so go carefully as you are but if nut height is wrong then most things won’t follow right . It might be out for only one or two strings
I always check nut height, then neck relief, then twelfth fret action then intonation