“Active conduct of and/or fighting in the Vietnam Conflict” shall mean service by any man or woman of the armed forces of the United States between February 28, 1961, and May 7, 1975, inclusive. Provided, however, that the extension of the date from August 5, 1964, to February 28, 1961, in the definition of the Vietnam Conflict shall not entitle any veteran who served between February 28, 1961, and August 5, 1964, to any bonus previously paid.