There is a ring around the case where the expander stopped expanding the case.
And a ring around the case at the base of the seated bullet.
Both rings have to do with how small in diameter the case was sized, the larger diameter of the expander and larger diameter of the bullet.
What this could mean is these cases were size with a under size die, meaning the cases were reduced .001 to .002 more in diameter than a standard die.
When you use mixed brass or range pickup brass this smaller diameter die ensures the case will have a tight grip on the bullet.
I have a under sized die and you normally see these marks on the cases that have thicker brass. If these cases were a old pair of blue jeans two sizes too smLee U Carbide Small Base Sizing Dieall this effect would be called 'midriff bulge'.
And I also would think twice before shooting someone else's reloads.
Preventing Bullet Setback
http://www.massreloading.com/setback.html
These cutaway .45 ACP cases below show that the case is expanded deeper than necessary for the 185gr bullet on the right.
Lee U Carbide Small Base Sizing Die
These dies undersize brass between .002" and .003" smaller than other Lee Carbide Sizing dies.
https://www.midwayusa.com/product/1012827841/lee-u-carbide-small-base-sizing-die