Yes, a company that makes API 6A valves can declare complaince with the standard. However, many custoemrs will not accept a declaration from the manufacturer. Do not trust them. Especially the China suppliers. So they rely on API to audit and certify the manufacturers product meets 6A. Upon successfully passing the audit, API grants a license to apply the API logo to the product. API provides a list of all approved manufacturers to their standards. It is called the Composite List and you can get it for free from their website. It is not imperative to get the API license to decalre 6A, but many end users expect it.