Should I divide my table into simpler ones or should I leave it the way it is?
No, breaking the table up that way is generally not a good idea unless you are talking about table partitioning in which case you have just one table as far as the overall design is concerned and the partitioning is a performance/administration difference.

With a separate distinct table per year you have the following problems, amongst others:


To query based on more than on year you have to UNION the tables back together (or take some other extra steps) which will make the resulting queries less efficient and less easy to maintain.
If extra years are needed later you will have to add new tables and update any views/procedures/queries/other that refer to multiple years as in the above point.
You will need to enforce (by adding database constraints if supported by the DB you are using or in your business logic) that the right rows go in the right tables which adds complexity.