If your tables contain the same content or at least are quite familiar together then it's often the best to concatenate these tables, like:
Load * From t1;
Load * From t2;
Load * From t3;
Commenly used are also combined keys between the tables to avoid the synthetic keys, like:
Year & '|' & Month & '|' & Ship as KEY
whereby I do not believe that those approach will be really suitable for you with 13 tables.
Many good postings about how to develop datamodels could you find here: