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.
"Counterfactuals" and "factuals" are terms that cannot be applied to "many worlds". We cannot single out events from a world. We can describe an event only in the context of a world.
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 their description as "actuality" is a conceit.
"Many worlds" is a "transcendentally real" formulation. The idea supposes that objects are carved out in Nature and correspond to their appearances, independently of that appearance.
In "transcendental idealism", however, there is no prospect for "many worlds", no prospect for objects as independent existents. 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 requires a template that isn't found in our world.