Even though, sometimes, the value that is the “total key to” a particular value, suitable for use in a hash-key that singularly leads to one value ... it might be almost-as-well to formulate a hash-key that potentially leads to a list of values, through which (an appropriate accessor-method) will have to search. A well-made accessor makes it easy / invisible. For that matter, you could have several hashrefs and multiple references. Basically, like what you have with the indexes that point into a DB table.
