Vintage, the timestamp of electricity production, refers to the generation date or time period when the renewable energy, tracked by an EAC, was produced. It's used by reporting frameworks and compliance schemes to impose vintage matching rules that determine which certificates are eligible for use. For example, "2025 Vintage" EACs carry the renewable attributes of electricity generated in 2025. As generation metadata is carried by each certificate, expiry timelines are applied from the point of generation onwards. After that period, the certificate's vintage is too old for usage and is technically worthless, which is also why older vintage EACs fetch lower prices as they approach expiry. Certain schemes may disallow certificates before the expiry date, even if they remain technically valid in a registry. For instance, Green-e® requires certificates to be no more than 21 months old relative to the reporting period, and RE100 recommends this as a "reasonable practice". This prevents companies from using old certificates to claim renewable energy use, ensuring claims reflect contemporary generation. Standard-driven vintage requirements like these is alsowhat creates a functional expiry for I-RECs, despite their perpetual registry validity.