COSS/COSP columns and fiscal year periods

Hello,

I am new to SAP and I'm trying to understand how the data is stored in the WKGXXX, WTGXXX ... columns in COSP and COSS.

Could anyone tell me what those columns represent and how is the data distributed among them if I am working with a fiscal year that has 24 posting periods or more? Or do those columns represent 12 calendar months and 4 special periods?

Many thanks,

Petru