Would it make sense to reduce some of those Chiefs to a lower rating, and let them get their 20 years? I'm not asking if it's possible. I'm asking if it would make sense.
The reason I bring this up is because many years ago a friend of the family was an air force lieutenant colonel with 17 years in. And he was passed for promotion to full colonel.
The air force let him serve 3 more years as a master sergeant.
If you accept an administrative reduction in rank then when you retire you get retirement pay for the highest rank attained.