Actually, I'd be kind of glad if it wasn't. I bought it as a practical piece of glassware, and I'd be less inclined to use it if I thought it had any kind of value to it.
So was Miller's wrong, then, or is this jug just very very similar to a Whitefriars Studio piece?
Although I'm not 100% sure that the jug was made yesterday, though, as there's a fair bit of wear to the base and it doesn't look like the result of a sandpaper attack.