Amended return deadline
When is the deadline for a 2008 individual return filed in November 2009 but the tax was paid in May 2010?
When is the deadline for a 2008 individual return filed in November 2009 but the tax was paid in May 2010?

You can file as long as you like, and if you owe more money they will take it forever.
But refunds can only be received when a claim is made within 2 years from the date the tax is paid, which in your example would be May 2012.