Keep in mind fiscal year restarts at the end of September/start of October. This amendment forces spending passed in the July-August Congress of 2019 to wait until FY 2021 to add new spending, while spending passed in September 2019 would be able to go into effect less than a month later with the commencement of FY 2020.
Why would a spending bill passed later be able to go into effect earlier?
Because the amendment Yankee introduced pushes the earliest time back by a year
only for the Congress starting in July.