(1) the amount by which the amount contributed for the taxable year to a trust or trusts described in section
501 (c)(21) exceeds the amount of the deduction allowable to such person for such contributions for the taxable year under section
192, and
(2) the amount determined under this subsection for the preceding taxable year, reduced by the sum of
(A) the excess of the maximum amount allowable as a deduction under section
192 for the taxable year over the amount contributed to the trust or trusts for the taxable year, and
(B) amounts distributed from the trust to the contributor which were excess contributions for the preceding taxable year.