How to organize the tables of a MySQL database with several statistics data of several years?
Well , i would add a new column on the Statistics_Entry as your year column ! Next depending on the volume of your data i would partition that table using this column(this will speedup your query when using the year column as your predicate). 
 This lookup table can be a view ! 
I would not create a new table just for the year column, this would just make thing complicated ! in my opinion !