I think this depends on whether or not you intend to mass produce or reproduce some of your items. I could certainly make a similar piece of jewelry but it's highly unlikely I'd be able to get all the same components as an earlier piece, even if I wanted to. So nothing would be identical to an earlier piece, although it could have a similar look.
I don't claim everything I make is one of a kind. I use that term when there's a component I can't find again or can't afford again (the price of sterling and gold rising so high that some components are now out of reach). So if I know there's only one set of beads like that, or only one pendant like that (especially if I made it), I have integrity about calling it OOAK.
But if I struck on a design that looked successful and I wanted to keep producing it for wider sales, I wouldn't use that term even if I was the original designer.
I think we have to be honest with ourselves when we use the term. If we plan to create more of the same, even not exactly the same, it doesn't really qualify as OOAK. But if this is a one-time-only product, it sure does.