We can only see DNS records that your name servers expose. When you attempt to use a domain name your computer will do a DNS lookup against your name server, which the name server will respond to. We request all of the available DNS records from your name server - it's up to the configuration of your name server to tell us what records exist. Usually, it will just respond with root domain A records (domain.com, rather than subdomain.domain.com), MX records and maybe TXT records - there are often more records that aren't exposed. Some providers, such as Cloudflare, actively hide as many records as possible from a general lookup.