Correct. Since the amount shown with code W in box 12 of your W-2 is only $6,333.18, the $166.66 that did not get deposited into the HSA would not have been excluded from the amount in box 1 of your W-2, so the $166.66 has already been taxed properly on your 2016 tax return. The only amount that needs to be included in income on your 2019 tax return is the roughly $86 that is the sum of the interest and the compensation for lost tax savings.
