Do older versions of cards use the card types printed on the newest version?
He is a Merfolk regardless of what version you use. (Lord is an obsolete creature type.) To find the official text and characteristics of a card, you should use Gatherer.

205.3f Many cards were printed with subtypes that are now obsolete. Many cards have retroactively received subtypes. Use the Oracle card reference to determine what a card’s subtypes are.
108.1. Use the Oracle™ card reference when determining a card’s wording. A card’s Oracle text can be found using the Gatherer card database at Gatherer.Wizards.com.