I did not manage to read this yet, but there is this W3C Accessibility Maturity Model document at W3C:

The W3C Accessibility Maturity Model is a guide for organizations to evaluate and improve their business processes to produce digital products that are accessible to people with disabilities. Use of the W3C Accessibility Maturity Model will provide organizations informative guidance (guidance that is not normative and does not set requirements) on improving accessibility policies, processes, and outcomes.

⚠️ Despite being in the same folder URL as a Web Standard, and looking like a Web Standard, this is only a Working Group Note and hence has not necessary gotten W3C consensus.