The box 2a amount is the normal amount needed...as long as box 2a has a non-zero value in it, or is not blank.
Some states used to not require a value there, but some changes by some of the states, as to how they tax retirement income, or perhaps new state partial exemptions to some of your retirement income...those changes have generally required an amount to be put into box 16.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
