Section Rev 3103.10 - Amended Tax Returns and Claims For Refund(a) Any taxpayer amending an original gambling winnings tax return or claiming a refund of taxes previously paid shall:(1) File Form DP-300, gambling winnings tax return, for the particular tax year; and(2) Check off the box entitled "Amended Return".(b) Pursuant to RSA 21-J:29, claims for a refund or amended gambling winnings tax returns, other than those filed on constitutional grounds, shall be filed: (1) Within 3 years of the original due date of the tax; or(2) Within 2 years from the date the tax was paid, whichever is later.(c) The 2-year provision in (b)(2), above, shall not apply if the payment was the result of an assessment or demand for payment initiated by the department.(d) Claims for a refund or amended returns that are filed based on a claim that the statute is unconstitutional shall be filed, pursuant to RSA 21-J:29, within 120 days of the due date of the tax and not the due date of the return.N.H. Admin. Code § Rev 3103.10