avoiding unique key collisions across tables
You should separate the table on year to get faster insert's, updates or deletes because we expect lots lots lots lots lots lots off records in this table..

**But... your problem is precisely the reason why separating tables on meta data (year in your question) is an SQL anti pattern, you could not have giving us an better use case* 

If you want an better solution you should read about mysql partitioning see http://dev.mysql.com/doc/refman/5.5/en/partitioning.html