Strictly speaking, we ought not to ask whether an event has occurred or not - events only arise in the context of a world. And as far as worlds go, there is a distinction between worlds that are identical and worlds that are not. The former are uncountable.
That is, "counterfactuals" and "factuals" are terms that cannot be applied to "many worlds". We cannot single out events from a world. We can describe only whole worlds.
But there is a problem with that also. For it looks as though "many worlds" must be imaged or viewed from the context of only one world - the world that we know. As such, they appear as empty surrogates of our world, for which the term "actuality" is a conceit.
"Many worlds" is also a transcendentally real formulation. The idea supposes that objects are carved out in Nature and correspond to their appearances.
In transcendental idealism there is no prospect for "many worlds". The supposed idea is an incoherence. In TI objects are items of knowledge constructed from templates of experience. To premise the idea of other worlds, and the same but "other" selves, on the notion of our own world and the things that we find in it is not something that we would know how to do or even understand.