My question is the following:
Is it possible that an event which is in my past light cone is currently in another observer's future light cone?
(i.e. for an observer sitting at a point in the set of coordinates $(x, t = 0)$ for a spacetime diagram in my reference frame, where I occupy the origin $(0, 0)$)
In plain English, is it possible that something which happened to me has not 'happened' yet in every possible reference frame (and thus not happened yet for some hypothetical observer), or have things that 'happened', like an explosion or an earthquake, occured in some fundamental sense, and are therefore in every observer's past ( 'every observer' meaning every possible reference frame associated to points $(x, 0)$ in my reference frame, i.e. observers which are in my current present).
Apologies for the convoluted form of the question, I'd gladly accept simplifications to it.