There are some folks who are wondering whether their cases are approved in EB1,EB2 or EB3 category. Here is an excel file I have found which may be helpful to see the codes on your approval letter and figure on what category your GC is approved. Also in each category there are different codes based on your expertise. So help yourself.
http://www.ins.gov/graphics/aboutins/statistics/statyrbook96/table5.xls
http://www.ins.gov/graphics/aboutins/statistics/statyrbook96/table5.xls