The achieved value over a period of one year after completion should be estimated at the time of completion.
See “Methodological support for ERDF and Cohesion Fund result indicators in the field of transport post 2020” JASPERS (2021) : https://ec.europa.eu/regional_policy/sources/policy/evaluations/General Guidance/2021/transport-indicators/methodl_support_indicators_post_2020_en.pdf