GMAT Math

Interesting question.
I checked the OG13, and labeling in a clockwise manner seems more common, but there are also examples of counter-clockwise labeling.

Cheers,
Brent

Letters will always be sequential. For example, in rectangle ABCD, A will always touch B and D, whether clockwise or counterclockwise. A will never touch C. Beyond that, though, don't worry about it! If you're given a geometry problem without a diagram, it will never matter whether it's clockwise or counterclockwise.