How to NOT make a database

I am working with a database of volumes/surface of forest in France… I have several sheets, because in the middle the inventory system of course changed.

But what make me extremely angry is the layout and encoding of the fields..
Species: in some sheets we have the species name in French, in others in French with some other remarks, in other in capital…
Department: sometimes we have the name, sometimes we have the code…
Time: sometimes we have the year, sometimes the year is a column, sometimes the year is the “cycle” of the inventory (a different year in each department)..

£$%/&%&“£$”#####!!!|“££$”£$% !!!!!