If you really believe 20 calories is anymore than a drop in a bucket that would actually sway a pound of weight gain or loss you are mistaken. You do NOT have to be 99. anything percent accurate to lose weight using calorie restriction.
Whoever sold you that is either wrong or you have greatly misunderstood what they are saying. Or you haven’t actually followed calorie restriction for long enough to realize that your calorie needs and intake can fluctuate from day to day and that some days you do go over them and it will have very little impact on the scale the following day.
I intentionally restrict calories. I also eat when I am hungry and that even means at times I am over my calories that I am supposed to eat for the day.
Guess what, I still lose weight at a steady state. I also have a VERY good understanding of my nutrition as well as how adjustments impact my goal at the time.
Things that are not measured are hard to improve/adjust on the fly when they stop working.