Each local housing authority that receives a distribution must confirm its distribution by providing the agency with a copy of an executed bond purchase contract or alternative documentation deemed sufficient by the commission to evidence the reasonable likelihood that the distribution will be fully used. Any portion of such distribution which is not confirmed will be added to the allocation of the commission. Such confirmation must be received by the agency no later than June 1: Provided, That for 1983 such confirmation must be received no later than October 1, 1983. The agency shall provide written notice of any change in the distribution to the affected local housing authority prior to the effectiveness of any such change.