I can't make any sense of this. It has happened over there - so it's happened. How does it make a difference where I am standing. I'm not talking about my reality. I'm talking about reality. Things which have taken place and nothing can change that.
Without the light (or radiation), all you can say is that "something may have taken place everywhere".
Then there’s ER=EPR to try to conceptualize.
Whether/when I "know" about it is separate, and not what they're talking about.
The OP was referring to when a event happened though.
For the sake if the argument let's allow this body to be an light-hour away from us when it happened.
I think your logic is very weak here.
Things happen without us knowing about it, and without light from such events ever reaching us. We don't need to know it has happened for it to have happened.
An element of light traces out a worldline. On any worldline we can apply whatever labelling-of-points we want since relativity is a coordinate-independent theory. We can label the points of a worldline with greek letters, hieroglyphs, roman numerals, natural numbers, real numbers, whatever we like and in any order we like.
One can build an infinity of calculationally-useless or misleading sets of coordinates on these worldlines for things heavier/slower than light. But one can also build an infinity of calculationally-useful and non-misleading coordinates for them, and many of those make use of the invariant spacetime interval. The same applies to coordinates for massless things / things that move at the speed of light, even though the invariant spacetime interval for light in free-fall is always 0, even if it is in free-fall for billions of years (like light from distant quasars, or the cosmic microwave background).
A calculationally-useful ordering applies a monotonically increasing order from the start to the end of a worldline in a time-orientable manifold (our universe is time orientable: smaller and denser in the past, bigger and sparser in the future). For timelike worldlines (i.e., anything that is always slower than light), almost always the most useful ordering is proper time.
But we cannot calculate proper time on a null (lightlike) worldline, so we will want some other monotonically increasing ordering function on the worldline, and ideally one with which we can solve the geodesic equation. Such a family of orderings is not only known, but has been textbook material since 1970 (Spivak's introduction to differential geometry). It's the affine parametrization.
For lightlike observers there is thus a useful and well-defined notion of time: the affine (parameter) time. This is different from but analogous to the proper time available to timelike observers. We can do standard vector physics on a photon using affine time, e.g. we can calculate its phase at various points along its trip from point A to point B. (Indeed, talking about a photon's quantum wavefunction, the affine parameter is proportional to its phase). We can also take the derivative of position with respect to affine time as a momentum that accurately captures the gravitational redshift or blueshift between two points on the null worldline.
"Is"?