"Puerto Rico's Tax System Adjustment Act allowed participants and beneficiaries of retirement plans to pay tax at special rates on their plan benefits during a limited time ... To take advantage of this opportunity, participants and beneficiaries had to either receive a distribution from the plan or pre-pay tax on their plan benefit during that window.... On March 30, 2015, Puerto Rico ... [extended] the end of the window for taking advantage of the special tax rates until April 30, 2015."