If it is, the closed-captioning and the credits made the same mistake. :) And the closed captioning has given it as Cley since season 1. Can we assume it's a mistake? SyFy does the SyFy summaries, but the people producing the show do the credits. I'd think the latter would be the most reliable source.
What's was the official basis for determining that it's spelled "Clay"? I know it's never appeared on-screen up to last week's episode.
Unless Duncan or Nathan's other son are in the episode next week, the credits won't say. Are they? The actor playing Nathan is always in the upfront credits, which means that his name is never spelled on-screen.