Logic to read a file for different intervals

I need to develop a logic, where - I get 4 fixed file in 2, 5, 9, 11 months Except above I get monthly files for 1, 3, 4, 6, 7, 8, 10, 12.

Note: All files come with same name.

Now, I need to read these files accordingly every month and push data into a table. If I have files monthly, I will read it and push data to table directly. If I do not have a file for any of the period among 1, 3, 4, 6, 7, 8, 10, 12 then I need to consider 2nd month file (from table) for 3, 4 & 5th month file (from table) for 6, 7, 8 & 9th month file (from table) for 10 & 11th month file (from table) for 12, 1 reading.

I tried many ways, but unable to arrive at the correct results.

Your kind help needed.