What a 'real event horizon' should mean is quite hard to understand for me though. I would like to define it from the Black Hole itself but from the inside there won't be any noticeable event horizon as I understands it, and if defined from the outside it must involve a observer. Using something 'at rest' outside it, relative the gravitational potential, maybe? But that is our geodesic observer, 'free falling'. And how can I define that as the only 'true event horizon'? I can have as many identical Rindler observers I like, with all swearing to seeing the Event horizon, or would they? I'm not sure, I would assume them to see a same Unruh radiation though if being 'at rest' relative each other, and as any patch of SpaceTime should be as the next?

"An absolute horizon is only defined in an asymptotically flat spacetime — a spacetime which approaches flat space as one moves far away from any massive bodies. Examples of asymptotically flat spacetimes include Schwarzschild and Kerr black holes. The FRW universe — which is believed to be a good model for our universe — is generally not asymptotically flat. Nonetheless, we can think of an isolated object in an FRW universe as being nearly an isolated object in an asymptotically flat universe.

The definition of an absolute horizon is sometimes referred to as teleological, meaning that it cannot be known where the absolute horizon is without knowing the entire evolution of the universe, including the future. This is both an advantage and a disadvantage. The advantage is that this notion of a horizon is very geometrical, and does not depend on the observer, unlike apparent horizons, for example. The disadvantage is that it requires the full history (all the way into the future) of the spacetime to be known. In the case of numerical relativity, where a spacetime is simply being evolved into the future, only a finite portion of the spacetime can be known."

Maybe all event horizons, ignoring conceptual definitions, will be 'apparent Horizons'?