A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I don't see any native, easy, way to do it. Other apps/languages allow MMM to force all upper, but not excel.
I found this tip, haven't tried it, that may have the key for your answer:
Converting Coded Dates into Real Dates
**http://excel.tips.net/Pages/T007163\_Converting\_Coded\_Dates\_into\_Real\_Dates.html******