As Hc4361 indicates, only a minority of people are listed on 192.com. Most people aren't these days. That's because most people now take up the option to have their names omitted from the edited register.
All residents in a property (who're eligible to vote) are legally obliged to ensure that their name appears on the
full version of the electoral register (which can only be consulted, in person, at local council offices, with strict rules about the way that it's used). A non-resident landlord's name should not appear on the electoral register. (It would be a criminal offence to include his name on it for a property that he doesn't occupy).
A person needs to reside at an address with a “considerable degree of permanence” in order for their name to be included on the electoral register for that area:
http://www.electoralcommission.org.uk/faq/voting-and-registration/i-have-two-homes.-can-i-register-to-vote-at-both-addresses