While simultaneity conventions for inertial frames in flat spacetime (SR) are non-controversial, numerous questions, discussions, and debates in this forum indicate how confusing and controversial notions of simultaneity can be for more general cases. A couple of formal and true answers are generally unsatisfying to many: - Simultaneity is undefinable, in any preferred way, in general. It is never observable or measurable anyway. - You can pick any any event not in your past or future light cone to be a simultaneous event to your now. Except locally, there is no preference. (Sufficiently locally, one can argue for a preference for the Fermi-Normal simultaneity). I thought of a possibly useful way to classify simultaneity notions for fairly general spacetimes and observers (I assume an orientable spacetime). Of critical importance is that any sensible implementation of these notions for inertial observers in flat spacetime produce the same result. However, they may differ wildly in curved spacetimes and/or for non-inertial observers. I assume, in what follows, that any observer can be considered past/future eternal unless their world line encounters a singularity. 1) It is reasonable to expect that any event in your causal past (on or inside your past light cone) is simultaneous to some event in your past. 2) It is reasonable to expect that any event in your causal future (on or inside your future light cone) is simultaneous to some event in your future. Executing (1) in various ways produces a foliation (family of simultaneity surfaces) that at least covers the union of all of your past light cones (all events that are ever in your causal past). I propose to call such foliations past inclusive if they at least cover your total causal past, but may cover more; and past only if they cover nothing except your total causal past. Similarly, notion (2) leads to future inclusive and future only simultaneity conventions. Finally, one may require that simultaneity be designed to cover any event in your total causal past or future. Call these causal inclusive and causal only As mentioned, for inertial observers in flat spacetime, these are all the same, and the obvious implementation is Minkowski frames. Now consider these for the Oppenheimer-Snyder spacetime (asymptotically flat; collapsing space time region; interior and exterior SC regions eventually). I choose this for qualitative plausibility and to avoid the white hole region (the notions certainly apply to full SC geometry). A) Consider a distant, hovering, eternal, observer. Exterior SC type time slices represent an implementation of past-only simultaneity. No events on or inside the EH are covered. On the other hand, any future-only simultaneity implementation covers the interior, and indeed, is also a causal inclusive simultaneity. There are infinite such choices which can agree with local Fermi-Normal simultaneity. B) Consider an observer that is distant and hovering into eternal past, but at some moment free falls into the BH (late enough so they hit the singularity). For this observer, both past-only and future-only conventions include both interior and exterior events. However, past only covers only a portion of spacetime - ending with the past of the termination of free fall world line on the singularity. A future only simultaneity covers all of space time, and is thus also a causal inclusive simultaneity. In my opinion, it seems clearly desirable to favor causal inclusive simultaneity; and thus it is unfortunate that so much attention is paid to SC time slice simultaneity, which is exclusively a past-only simultaneity.