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Keep in mind that Excel is NOT a database system and should not be used as such. Its not designed to handle heavy loads of stored data and that could possibly explain why its slow to open. Excel is a spreadsheet software designed for number crunching and graphical display, not storing data. If you're simply storing entries for your job, I would recommend using something like Microsoft Access, which is designed for storing data. Its a little more difficult to use, but once you get the basics down its not that hard. And it won't be slow like Excel since its designed to work with heavier loads.

I would make a copy of each tab and paste them to another excel file and name the file by the year.