The whois information is incomplete, because only the server where the registration data is stored will show complete information unless of course legislation forbids showing information about private individual, like for example EU residents.
In some legislations anonymizer services are forbidden, but there is a lot of legislations where anonymizer services are allowed.
All other whois servers than registrar's own whois server show limited information so malicious users have harder time to harvest addresses or phone numbers for mass marketing or other illegal activities.