The notion of a horizon in general relativity is subtle and depends on fine distinctions.
A (compact, orientable, spacelike) surface always has two independent forward-in-time pointing, lightlike, normal directions.
For example, a (spacelike) sphere in Minkowski space has lightlike vectors pointing inward and outward along the radial direction.
For example, in the case of a perturbed black hole, the EH and the AH generally do not coincide as long as either horizon fluctuates.
Event horizons can, in principle, arise and evolve in exactly flat regions of spacetime, having no black hole inside, if a hollow spherically symmetric thin shell of matter is collapsing in a vacuum spacetime.
Bob Geroch has pointed out that if all the stars in the Milky Way gradually aggregate towards the Galactic Center while keeping their proportionate distances from each other, they will all fall within their joint Schwarzschild radius long before they are forced to collide.
[4] The emission of Hawking radiation violates the weak and the null energy condition.
That is, the location and even existence of an apparent horizon depends on the way spacetime is divided into space and time.