Dan,
The IRS's statute of limitations to collect a balance where fraud is not involved is 10 years from the date of assessed tax. The IRS initially has 3 years to assess the tax. Certain actions, like an agreed upon extension, can extend that 10 year period. In your case, The IRS had until 2001 to assess the tax, which would have then created a 10 year period beginning on January 1, 2001. This would reasonably fall in the same time as the December 2011 cut-off period that you received.
I am limited to only advising you that the date given to you seems reasonable. If you are not satisfied with the information ATR has given you, you may always call the IRS yourself at XXX-XXX-XXXX to inquire about the status of your specific account. Please let me know if you have further questions.
Regards,
Mark D
Tax Preparer
MBA, CTEC Registered, CPA Firm Experience with Business and Individual Tax Returns and Issues