Correct Front Bumper Arms

[Dave Pratt - IL]

According to the Judging Standards, the front bumper arms changed from square ends to rounded ends in 1931. The square ones were used until mid-'31. The rounded ends could be used starting in early '31. What I don't understand is if this is referring to both ends or only one. Seaching through my stack of arms, I find 3 versions:
- Both ends square
- Both ends rounded
- One end rounded and one end square

What am I missing?