The $2 bills was officially discontinued in August 1966 until 1976 when the Treasury Department reintroduced the $2 bill as part of the United States Bicentennial celebration.
We know for a fact that 1976 $2 bills were released into circulation on April 13, 1976. We know this because tens of thousands of people took their new 1976 $2 bills to the Post Office to have them cancelled, usually with a 13 cent stamp.
The 13 cent stamp was used because that is how much it cost to mail a letter in 1976. Stamped 1976 $2 bills typically sell for about $5 each. If they were stamped in an exotic place then the value might be closer to something like $8.