The CRA just sent me a letter requesting support documentation for a deduction on Line 25600. My TurboTax T1 includes an "Additional deductions - line 25600" statement that lists an amount for "15% of U.S. social security benefits reported on line 11500" (which I understand) and also second amount for "Other income exempt under a tax treaty" (which I cannot figure out the source of). Where might this second amount come from?
