If the trust had income this year and was distributing more than the income earned during the tax period, the reporting would depend upon whether the income distribution was mandated by the terms of the trust or whether the distribution was discretionary (i.e., at the discretion of the trustee).
Regardless, amounts actually paid or credited are second tier distributions and reported as such. Amounts of income that are required to be distributed are first tier distributions and the beneficiaries are responsible for any tax due whether the income is actually distributed or not.
K-1s are used to report items of income, gain, credits, and deductions; they are not used to report distributions of trust corpus.
