Purpose for purpose
Building something for a purpose and maintaining it for a purpose are two different things. The purpose may change, in which case you may need a new system. The system may change, in which case you need to change the system to fit the purpose, or to update your purpose.
In both cases, “is it fit for purpose?” is as good a question as any.
Is the system meeting the purpose? Is the purpose meeting the system? And, more importantly, “Is the purpose meeting the purpose?”