As explained in my article, when a taxpayer has unfiled returns, the IRS will file them in replacement....which is called an SFR, or Substitute for Return. The IRS will put the taxpayer in the worst possible tax bracket by only giving the standard deduction and minimum exemptions. Then add on penalties for not filing on time, paying on time, and other miscellaneous penalties plus interest and the tax liability can get out of hand quickly!
There are a couple of different ways to know if an SFR has been filed. First, a tax professional can discern if an SFR has been filed by looking at IRS collection letters. At the top of the letter the tax type is stated, and oftentimes, the IRS will call an SFR a form "1040A". This method is not 100% and may get confusing as 1040A also refers to a simplified version of the 1040 tax return. A 1040A is one step up from a 1040EZ and one step down from a straight 1040 in complexity. The other way to know is a qualified tax professional can order your transcripts and can then determine if an SFR has been filed by looking at the account history. This is the best way to find out for sure.
If you have unfiled returns, you need a qualified tax professional to protest the SFRs. You need someone who deals with the IRS on a daily basis, in order to help you get back on the right path. Seek help immediately.