No worries as there is no such animal as "Open" or "Limited" class.
The classes are U, D, C, B, A, M, and GM. Class represents your shooting ability compared to others.
"Divisions" are determined by the equipment you use for a particular match.
(Not jumping on you, it is a common confusion)
I blame Charlie Funk for it and those familiar with the early development of EZ-score will understand why.