If you normally have a refund coming back they may not come after you since after 3 years the statute expires for you to collect the refund.
My recommendation would be to contact the IRS and request a wage and income transcript. This would provide you with the information from your W2s, interest income and other sources of income. You could then use this to prepare your tax returns for 2005 thru 2009. This would mean that the refunds you may be entitled to would not be lost - note the 2005 and 2006 are already past that timeperiod and the 2007 will expire on April 15, 2011.
Additionally if by any chance you owe for one or more of those years, the statute of limitations never runs out for IRS to collect. It could be with moving IRS has lost where you are. Since you have now filed a 2010 though they will find you and come looking for you for any balance dues. Right now if you have refunds in some years and owe in others they may be able to offset one another. If you wait a few years the refunds will be gone but the balance dues will still remain.
Even with the 2005 and 2006 tax years expired, I would still recommend that you file these returns. If you never file, the statute never runs out. If you file after 3 years they cannot come after if they find something later on.
The can reach the IRS at 1-800-829-1040 or you can also request transcripts on their website at www.irs.gov. If you are going to be working with a tax preparer to prepare these returns and use either an EA or a CPA they will be able to request the documentation for you also if you sign a power of attorney for them.
Your situation is not unusual at all. The key is to get caught up and make payment arrangements with the IRS is by some chance you end up owing.
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