Excel and comparing data

Working on inventory comparisons for 2 months. I have output of over 120,000 rows. Each row represents a stock # however the stocks are duplicated and may be assigned to different G/L accounts (projects). I’m trying to analyze the change from the previous month to the current, and am having to do this pretty much manually based on G/L (I have no primary keys and because items duplicate can’t concatenate one). Any suggestions out there?