Does REC/GO retirement start on the purchase date, or can certificates be applied to a specific reporting year?

If you purchase RECs or GOs, the key factor is not the purchase date but the reporting year you want them to apply to. The certificates must match the generation period allowed under your reporting standard, usually within the same calendar year or up to 12 months before or after, depending on the GHG Protocol or other relevant guidelines.

You can buy them in advance or retroactively, but they must be retired for the correct reporting year to be valid. So if you purchase 500 MWh in November, you can apply them to the current year or the next, as long as the generation and retirement dates align with your reporting boundaries.