Depends on who took them! I have watched them scrotal measure at the Beef Expo, and have seen the tape pulled "taunt" sometimes, while others would loosely taken. No fault of the operator, just depends on how the bull cooperates. Depedns on if the tape operator is having a good time or not, etc. I have also seen scrotals taken by one person who always pulls it tight, while other operators use a more gentle touch. A centimeter isn't much to vary.
Scrotal measurements also vary by weather. Is it hot? Was it cold? Was the bull just washed when it was 10 degrees?
Kinda like ultrasound carcass info, the operator is crucial. It can vary much more than anyone realizes.
So I guess, although I look at them, they are just a single tool, that is just a small part of a big equation.