A one-time audit only reflects a site’s accessibility at that specific moment; every new blog post, product page, or feature release is an opportunity to reintroduce a barrier, whether that is a missing alt tag on a new image or a poorly built new interactive widget. Ongoing monitoring typically combines automated scanning on a recurring schedule (weekly or monthly, or on every deployment) with periodic manual spot-checks of new or changed pages.
Organizations serious about long-term compliance tend to treat monitoring as a standing program with clear ownership, not a project that ends once the initial remediation is complete.