41 C.F.R. § 302-17.51
When to provide amended tax information to the agency
Employees should submit amended tax information to their agency under the one-year process whenever the tax information previously provided changes, and employees should continue to amend the information until they have received the last W-2 from their agency in connection with a specific relocation. In particular, employees should submit amended information whenever:
(a) Their filing status changes;
(b) Their income changes enough that their income, including WTA and RITA, might put the employee into a different tax bracket; or
(c) They have taxable relocation expenses in a second or third calendar year.