How to 100% know if a dial is aftermarket?

[Ninja Master]

Hi all

I know there have been posts like this in the past, but the answers are all a bit vague.

Let's say I buy a second hand/grey OP with a red dial (discontinued, so kind of expensive now).

How do I know it's not a more common model with an aftermarket dial?

Is there a way to know 100% either pre or post purchase?

Thanks