Absolutely. In fact, if you have been providing over 50% of your mother's support for several years, you should go back and amend your returns for 2003, 2004 and 2005 and claim her as a dependent for those years as well. I have done such amendments over twenty times over the past 15 years and the IRS has never challenged their validity.
Do not forget to amend the state returns as well.
If you need help, contact me at
[email protected] to discuss fees.
It is too late to amend the returns for 2002 and earlier, as there is a 3-year statute of limitations for claiming additional refunds on tax return.