Posting Dates incorrect in setup

Our client has an unusual situation in that the fiscal period date setup is incorrect. Following are the facts:

1. Fiscal Period 2012 is setup with 12 monthly periods with beginning and ending dates of 01/01/13 and 12/31/13

2. Fiscal Period 2013 is setup with 12 monthly periods with beginning and ending dates of 01/01/12 and 12/31/12

3. 2012 Year End Closing has been performed and consequently is in historical status (last closing period displays as 12/31/2013)

4. 2013 is in open status with period date ranges 1/1/12 - 12/31/12

I attempted to change the dates in fiscal period setup with no luck.  Message displays stating that the date range cannot be outside the fiscal period.  They didn't find the issue until they attempted to process a 2012 trial balance and now have 2013 transactions already entered.

Any input on a resolution would be appreciated.

Thanks,

Debi