Yeah that would be my guess too, a bit hard to see as you say but unless you permanantly fix the biceps in the bells you can swap as you go along.
The CRL (costume reference library) states:
Shoulder Armor
One on each shoulder.
The shoulders are considered effectively symmetrical.
They may be worn interchangeably on the left and right shoulders
Shoulders have a black elastic strap that wraps around the inside of the bicep.
OPTIONAL Level two certification (if applicable):
OPTIONAL Level three certification (if applicable):
There should be a minimal gap between the shoulder armor and the chest/back plates.