The idea of fact is complex in its epistemic, metaphysical and linguistic connotations, but in the end it has compelling force, and the power to shock when the predicted practical effects are not actualized.
The concept would rely on a power set (P) or set of all possible sets of facts (F), containing individual or elementary facts, x, mapped to the worlds, W, where these facts exist.
In probability theory, the existence of different set cardinality for the natural and real numbers prevents assigning probabilities to each possible set of outcomes, and the idea of sigma-algebra is introduced as a compromise to limit the measurement of probabilities to only those sets in the power set that are measurable.
This idea might not have been introduced in the philosophical approach to facts. It makes no sense in a way since facts are not always quantifiable.
However, facts are indeed mapped (measured) to at least an ordinal or scale of relative importance, and some are discarded, while other are used.
In this regard, some facts are 'not F-measurable' (they have no probability - read, 'significance' or 'qualitative value') while others are highly weighted for importance or in terms of utils in economics, for instance.
I wonder if including the concept of 'measurable' or 'assignable' sets through sigma algebras (sets of events we are subjectively interested in) within the power set of facts could enrich this approach to facts as mappings between propositions and worlds, perhaps introducing injectivity in a more consistent manner.