The claim here is that if a theory/model is quasi-true then it can be quasi- explanatory, but just as the quasi-truthfulness of a theory doesn't automatically give a measure of external correspondence truth so too quasi- explanation does not imply the degree of overlap with a correspondence explanation. The notion of quasi-truth is irrevocably tethered to the notion of a domain of applicability, so a quasi-true theory does not imply much about the correspondence true theory outside of that domain other than within the domain the two must agree empirically. However, the domain can be relatively small, hence we cannot simply make inductive extensions of quasi-true theories as being approximately true therefore looking similar to the correspondence true theories outside of the domain. The cumulative aspect of science comes from amassing a large number of domains. In the context of explanation this is also the case, because a quasi-explanation captures modal information in a domain does not mean that its ontology will be similar to the ultimate correspondence ontology. The pattern on the curtain does not tell us what the wizard will look like.
However, what we do have is an increasing network of modal connections and overlapping perspectives that constrain how the correspondence ontic explanations must behave in those domains. We should not make the mistake of taking a holistic definition in reference to a domain and turning that into an approximation without reference to a domain. Nihil models are not approximately explanatory, they are quasi- explanatory in a domain and that is why they remain (quasi) explanatory even if new explanations come along which have wider domains. In discussing a model that describes the electron as point-like da Costa and French state:
It is not the case that the description stands free of the theoretical context, so that we can talk of this idealised electron as a separate entity, existing in some possible world perhaps; rather, the idealisation is bound to the model. (Da Costa & French, 2003 chapter 8)
It is this kind of holism that the account of explanation presented here is attempting to capture. Idealisations, abstractions, and fictions are essential aspects that result from, and are often necessary for, the construction of a gestalt which allows modal structure to be represented. It is the overall model in which the fiction plays a role that is quasi-explanatory relative to a domain.
Fictions in models work because of the way they interlock with other aspects of the model to capture modal structure. It is the totality which is necessary. This is not to say nothing can be said about the parts of a model and how they achieve this feat, far from it, but to understand a fiction the perspective must be understood. This holism runs counter to the Galilean intuition. It also fits nicely with the idea that models as a whole should be regarded as fictions, if the whole fictional model captures modal relations then specific fictions within it play their role in their place in the structure of the larger fiction not in isolation. The fictions within a model work because of their relations to the other parts of the model, but there is no ontological divide internal to a given model, rather the whole is a fiction. Just as the play within a play in Hamlet is not a different type of thing to Hamlet itself, and its significance can only be see in relation to the wider play. Plucking it out and examining it in isolation would not reveal its true meaning.
To quote da Costa & French again:
To describe an electron as if it were a point particle is to lay down a bundle of properties that have meaning only within a model or, more generally, a structure; thus the "as if" character of such idealization terms gets shifted to that of the embedding context. (Da Costa & French 2003, Chapter 8)
Fictions work because of the structural context of a particular model. This is why a fiction can be explanatory in one model but not explanatory in another model. The fiction works to capture modal information in the contextualising environment of a fictional world, a fiction within a fiction to facilitate representing modal structure. This is why the correct ontology for models is that of fictions, to avoid othering the non-referring terms in
them. Idealisations and abstractions cannot be understood in isolation, they must always be evaluated relative to an explanandum that they play a role in addressing. It is only then that we can see in a heterogeneous manner how each individual idealisation still keeps some essential property of the real-world, or surrealistically represents some appearance of the world. Structural contextualisation of the properties of entities within models with reference to an explanandum is essential for explicating the ways in which "lies" told in models can get to greater truths.
This is why attempts to sub-divide theories and models into the "bits that do the work" and the parts that don't will always be inadequate. Part of why we cannot predict which parts of a theory will be preserved by a successor is that we don't know the context in which terms in the predecessor will be put into in the new theory, and without the structural context of terms and properties in models and theories they are meaningless. One suspects that the wonderment at how idealisations in models can work is produced by plucking them out, de-contextualising them from the larger structure and commenting on how curious they look on their own. To return to our literary analogy, this is like putting Count Dracula into The Old Curiosity Shop and then remarking how out of place he looks.