Calyx Global sometimes gives multiple ratings for a project based on the vintage of the credits rather than one rating for the entire life of the project. The vintage refers to the year when the claimed emission reductions or removals occurred. Conditions can change during a project's lifetime, and giving ratings for different time periods allows Calyx Global to provide our customers with more accurate evaluations of the project's greenhouse gas (GHG) integrity over time. This is also true for Sustainable Development Goal (SDG) contributions, where a project's impact can change over time. Different project categories can have different concerns about changes within a project's lifetime; we provide some examples below.