SIDN not associated with the sale of subdomains under co.nl
The most important thing to be aware of is that SIDN, the registry for the .nl domain, is not involved in the sale of subdomain labels under co.nl. Co.nl is therefore quite different from, for example, co.uk, which is an extension option offered by the UK's country-code domain registry, Nominet. Anyone is entitled to register a domain name directly below .nl and any registrant of a .nl domain is entitled to create subdomains under their registered domain name. For example, Startpagina can create subdomains under startpagina.nl, such as games.startpagina.nl. That is exactly what the registrant of the .nl domain name co.nl is doing. If you register a subdomain label under co.nl, you are not entering into a contract with SIDN. Your agreement is with the registrant of co.nl, who in turn has a contract with SIDN and is therefore bound by SIDN's General Terms and Conditions.
Co.nl subdomain labels are not .nl domain names
Users should also recognise that, when they register a co.nl label, they are NOT registering a .nl domain name. They are buying a service from a company that has registered the .nl domain name co.nl. We advise users to think carefully about how and from whom it is best to obtain DNS services. There are now about a thousand domain name extensions under which domain names can be registered, including the Dutch country-code extension .nl, which is managed by SIDN. All those extensions (known as TLDs) are formally registered with IANA.
Naturally anyone is free to decide against registering a domain name directly below one of the thousand official extensions, and to register a subdomain with an alternative service provider instead. However, we advise registrants to think carefully before acting, not only about the price, but also about the service conditions.